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1.
Structure ; 24(12): 2152-2162, 2016 12 06.
Artigo em Inglês | MEDLINE | ID: mdl-27839947

RESUMO

Ras-interacting protein 1 (Rasip1) is an endothelial-specific Rap1 and Ras effector, important for vascular development and angiogenesis. Here, we report the crystal structure of the Rasip1 RA domain (RRA) alone, revealing the basis of dimerization, and in complex with Rap1 at 2.8 Å resolution. In contrast to most RA domains, RRA formed a dimer that can bind two Rap1 (KD = 0.9 µM) or Ras (KD = 2.2 µM) molecules. We solved the Rap1-RRA complex and found that Rasip1 binds Rap1 in the Switch I region, and Rap1 binding induces few conformation changes to Rasip1 stabilizing a ß strand and an unstructured loop. Our data explain how Rasip1 can act as a Rap1 and Ras effector and show that Rasip1 defines a subgroup of dimeric RA domains that could mediate cooperative binding to membrane-associated Ras superfamily members.


Assuntos
Peptídeos e Proteínas de Sinalização Intracelular/química , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas rap1 de Ligação ao GTP/metabolismo , Proteínas ras/metabolismo , Sítios de Ligação , Dimerização , Humanos , Modelos Moleculares , Ligação Proteica , Domínios Proteicos , Estrutura Secundária de Proteína , Proteínas rap1 de Ligação ao GTP/química , Proteínas ras/química
2.
J Biol Chem ; 288(33): 23639-49, 2013 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-23814056

RESUMO

Loss of function mutation in Krev interaction trapped 1 (KRIT1) causes autosomal dominant familial cerebral cavernous malformations and disrupts cardiovascular development. The biological function of KRIT1 requires that its FERM (band 4.1, ezrin, radixin, moesin) domain physically interact with both the small GTPase Rap1 and the cytoplasmic tail of the Heart of glass (HEG1) membrane anchor. In this study, we show that the KRIT1 FERM domain can bind both Rap1 and HEG1 simultaneously, and we solved the crystal structure of the KRIT1-Rap1-HEG1 ternary complex. Rap1 binds on the surface of the F1 and F2 subdomains, in an interaction that leaves its Switch II region accessible to other potential effectors. HEG1 binds in a hydrophobic pocket at the KRIT1 F1 and F3 interface, and there is no overlap with the Rap1-binding site. Indeed, the affinity of KRIT1 or the KRIT1-Rap1 complex for HEG1 is comparable (Kd = 1.2 and 0.96 µm, respectively) showing that there is no competition between the two sites. Furthermore, analysis of this structure revealed a specific ionic interaction between the F2 lobe of KRIT1 and Rap1 that could explain the remarkable Rap1 specificity of KRIT1. This structural insight enabled design of KRIT1(K570I), a mutant that binds Rap1 with 8-fold lower affinity and exhibits increased binding to HRas. These data show that HEG1 can recruit the Rap1-KRIT complex to the plasma membrane where Rap1's Switch II region remains accessible and reveals an important determinant of KRIT1's specificity for Rap1.


Assuntos
Glicoproteínas de Membrana/química , Glicoproteínas de Membrana/metabolismo , Proteínas de Membrana/química , Proteínas de Membrana/metabolismo , Proteínas Associadas aos Microtúbulos/química , Proteínas Associadas aos Microtúbulos/metabolismo , Complexos Multiproteicos/química , Complexos Multiproteicos/metabolismo , Proteínas Proto-Oncogênicas/química , Proteínas Proto-Oncogênicas/metabolismo , Proteínas de Ligação a Telômeros/metabolismo , Sítios de Ligação , Cristalografia por Raios X , Ácido Glutâmico/metabolismo , Humanos , Íons , Proteína KRIT1 , Modelos Moleculares , Ligação Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Proteínas Proto-Oncogênicas p21(ras)/metabolismo , Complexo Shelterina , Relação Estrutura-Atividade
3.
J Biol Chem ; 284(8): 5119-27, 2009 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-19098287

RESUMO

Rap1 small GTPases interact with Rap1-GTP-interacting adaptor molecule (RIAM), a member of the MRL (Mig-10/RIAM/Lamellipodin) protein family, to promote talin-dependent integrin activation. Here, we show that MRL proteins function as scaffolds that connect the membrane targeting sequences in Ras GTPases to talin, thereby recruiting talin to the plasma membrane and activating integrins. The MRL proteins bound directly to talin via short, N-terminal sequences predicted to form amphipathic helices. RIAM-induced integrin activation required both its capacity to bind to Rap1 and to talin. Moreover, we constructed a minimized 50-residue Rap-RIAM module containing the talin binding site of RIAM joined to the membrane-targeting sequence of Rap1A. This minimized Rap-RIAM module was sufficient to target talin to the plasma membrane and to mediate integrin activation, even in the absence of Rap1 activity. We identified a short talin binding sequence in Lamellipodin (Lpd), another MRL protein; talin binding Lpd sequence joined to a Rap1 membrane-targeting sequence is sufficient to recruit talin and activate integrins. These data establish the mechanism whereby MRL proteins interact with both talin and Ras GTPases to activate integrins.


Assuntos
Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Proteínas de Transporte/metabolismo , Membrana Celular/metabolismo , Integrinas/metabolismo , Proteínas de Membrana/metabolismo , Talina/metabolismo , Proteínas rap1 de Ligação ao GTP/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Sequência de Aminoácidos/fisiologia , Animais , Sítios de Ligação/fisiologia , Células CHO , Proteínas de Transporte/genética , Membrana Celular/genética , Cricetinae , Cricetulus , Humanos , Integrinas/genética , Proteínas de Membrana/genética , Sinais Direcionadores de Proteínas , Estrutura Terciária de Proteína/fisiologia , Transporte Proteico/fisiologia , Proteínas Proto-Oncogênicas p21(ras)/genética , Proteínas Proto-Oncogênicas p21(ras)/metabolismo , Talina/genética , Proteínas rap1 de Ligação ao GTP/genética
4.
Curr Biol ; 16(18): 1796-806, 2006 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-16979556

RESUMO

BACKGROUND: Integrin receptors, composed of transmembrane alpha and beta subunits, are essential for the development and functioning of multicellular animals. Agonist stimulation leads cells to regulate integrin affinity ("activation"), thus controlling cell adhesion and migration, controlling extracellular-matrix assembly, and contributing to angiogenesis, tumor cell metastasis, inflammation, the immune response, and hemostasis. A final step in integrin activation is the binding of talin, a cytoskeletal protein, to integrin beta cytoplasmic domains. Many different signaling molecules that regulate integrin affinity have been described, but a pathway that connects agonist stimulation to talin binding and activation has not been mapped. RESULTS: We used forward, reverse, and synthetic genetics to engineer and order an integrin activation pathway in cells expressing a prototype activatable integrin, platelet alphaIIbbeta3. Phorbol myristate acetate (PMA) activated alphaIIbbeta3 only after the increased expression of both recombinant protein kinase Calpha (PKCalpha) and talin to levels approximating those in platelets. Inhibition of Rap1 GTPase reduced alphaIIbbeta3 activation, whereas activated Rap1A(G12V) bypassed the requirement for PKC, establishing that Rap1 is downstream of PKC. Talin binding to integrins mediates Rap1-induced activation because Rap1A(G12V) failed to activate alphaIIbbeta3 in cells expressing integrin binding-defective talin (W359A). Rap1 activated integrins by forming an integrin-associated complex containing talin in combination with the Rap effector, RIAM. Furthermore, siRNA-mediated knockdown of RIAM blocked integrin activation. CONCLUSIONS: We have, for the first time, ordered a pathway from agonist stimulation to integrin activation and established the Rap1-induced formation of an "integrin activation complex," containing RIAM and talin, that binds to and activates the integrin.


Assuntos
Complexo Glicoproteico GPIIb-IIIa de Plaquetas/agonistas , Transdução de Sinais/fisiologia , Animais , Sítios de Ligação , Plaquetas/metabolismo , Células CHO , Cricetinae , Cricetulus , Proteínas de Fluorescência Verde/análise , Humanos , Modelos Biológicos , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/metabolismo , Proteína Quinase C/metabolismo , Proteínas Recombinantes de Fusão/análise , Transdução de Sinais/efeitos dos fármacos , Talina/metabolismo , Talina/fisiologia , Acetato de Tetradecanoilforbol/farmacologia , Proteínas rap1 de Ligação ao GTP/metabolismo , Proteínas rap1 de Ligação ao GTP/fisiologia
5.
Biochem J ; 378(Pt 3): 1079-82, 2004 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-14690453

RESUMO

Chemical or enzymic reduction/oxidation of integrin cysteine residues (e.g. by reducing agents and protein disulphide isomerase) may be a mechanism for regulating integrin function. It has also been proposed that unique cysteine residues in the integrin beta3 subunit are involved in the regulation of alphaIIbbeta3. In the present study, we studied systematically the role of disulphide bonds in beta3 on the ligand-binding function of alphaIIbbeta3 by mutating individual cysteine residues of beta3 to serine. We found that the disulphide bonds that are critical for alphaIIbbeta3 regulation are clustered within the EGF (epidermal growth factor) domains. Interestingly, disrupting only a single disulphide bond in the EGF domains was enough to activate alphaIIbbeta3 fully. In contrast, only two (of 13) disulphide bonds tested outside the EGF domains activated alphaIIbbeta3. These results suggest that the disulphide bonds in the EGF domains should be intact to keep alphaIIbbeta3 in an inactive state, and that there is no unique cysteine residue in the EGF domain critical for regulating the receptor. The cysteine residues in the EGF domains are potential targets for chemical or enzymic reduction.


Assuntos
Cisteína/fisiologia , Fator de Crescimento Epidérmico/química , Integrina beta3/química , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/química , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/metabolismo , Animais , Células CHO , Cricetinae , Cricetulus , Cisteína/genética , Dissulfetos/química , Fibrinogênio/metabolismo , Humanos , Integrina beta3/genética , Mutagênese Sítio-Dirigida , Estrutura Terciária de Proteína
6.
J Cell Biochem ; 88(3): 506-20, 2003 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-12532327

RESUMO

The basement membrane protein laminin-5 promotes cell adhesion and migration. The carboxyl-terminal G3 domain in the alpha3 chain is essential for the unique activity of laminin-5. To investigate the function of the G3 domain, we prepared various recombinant laminin-5 forms with a partially deleted or mutated G3 domain. The deletion of the carboxyl-terminal 28 amino acids (region III) markedly decreased the cell adhesion activity with a slight loss of the cell motility activity toward BRL and EJ-1 cells. This change was attributed to the loss of Lys-Arg-Asp sequence. Further deletion of 83 amino acids (region II) led to almost complete loss of the cell motility activity. All charged amino acid residues tested in this region were not responsible for the activity loss. These results suggest that the G3 domain contains two distinct regions that differently regulate cell adhesion and migration. Analysis of laminin-5 receptors showed that integrins alpha3beta1, alpha6beta1, and alpha6beta4 had different but synergistic effects on cell adhesion and migration on laminin-5. However, the structural change of the G3 domain appeared not to change integrin specificity. The present study demonstrates that the G3 domain in laminin-5 plays a central role to produce different biological effects on cells.


Assuntos
Adesão Celular/fisiologia , Movimento Celular/fisiologia , Laminina/metabolismo , Mutação , Proteínas Recombinantes/metabolismo , Sequência de Aminoácidos , Animais , Linhagem Celular , Tamanho Celular , Humanos , Integrinas/metabolismo , Laminina/química , Laminina/genética , Camundongos , Dados de Sequência Molecular , Estrutura Terciária de Proteína , Proteínas Recombinantes/genética
7.
Hybrid Hybridomics ; 21(4): 253-60, 2002 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-12193278

RESUMO

Cell adhesion receptors of the integrin superfamily can be expressed in different affinity states towards their ligands. It has been previously demonstrated that beta(1) integrins alpha4beta(1) and alpha5beta(1) are expressed in a nonligand binding form by human hemopoietic progenitor cells but can be activated into a ligand binding form by a variety of stimuli including intracellular stimuli generated by cytokine receptors and extracellular stimuli generated by function-activating anti-beta(1) integrin monoclonal antibodies (MAbs). In both instances, the activation of beta(1) integrins is believed to be the result of conformational changes propagating along the beta(1) integrin chain which in turn increase accessibility to the ligand. A cluster of either function-activating or function-inhibiting anti-beta(1) integrin MAbs have been shown to bind within a 12 amino acid long regulatory loop between residues 207 and 218 of the human beta(1) integrin chain. We describe in this report the first MAb (96.9H9) specific for this regulatory loop whose binding is cation-dependent and requires either Ca(2+) or Mn(2+) but not Mg(2+). In addition, the activation of alpha4beta(1) and alpha5beta(1) integrins by 96.9H9 is a two-step process with distinct cation requirements. Whereas Ca(2+) is sufficient to promote binding of the antibody to the beta(1) integrin chain, Mg(2+) is necessary for activating function following 96.9H9 binding. Our data therefore suggest that the regulatory epitope of the human beta(1) integrin chain is flexible with multiple conformations according to the cationic environment.


Assuntos
Anticorpos Monoclonais , Integrina beta1/imunologia , Animais , Especificidade de Anticorpos , Sítios de Ligação , Células CHO , Cátions Bivalentes/metabolismo , Adesão Celular/imunologia , Linhagem Celular , Cricetinae , Mapeamento de Epitopos , Epitopos/química , Epitopos/metabolismo , Fibronectinas/metabolismo , Humanos , Hibridomas/imunologia , Integrina beta1/química , Integrina beta1/metabolismo , Ligantes , Camundongos , Camundongos Endogâmicos BALB C , Conformação Proteica , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/imunologia , Proteínas Recombinantes de Fusão/metabolismo
8.
J Cell Sci ; 115(Pt 10): 2199-206, 2002 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-11973360

RESUMO

Integrins mediate cell adhesion and signal transduction at focal adhesions. Here we investigate the roles of integrin beta subunits in the regulation of actin cytoskeletal structure and the activities of Rho and Rac. The overexpression of beta3 integrin in Chinese hamster ovary cells enhances Rho activity and stress fiber formation, whereas the overexpression of beta1 integrin increases Rac activity and lamellipodia formation. The overexpression of a mutant beta1-3-1 integrin, in which the extracellular I-domain-like sequence of beta1 integrin has been replaced with the corresponding sequence of beta3 integrin, also enhances Rho activity and the formation of stress fibers. Our results demonstrate that beta1 and beta3 integrins differentially regulate the activities of Rho family GTPases and that the extracellular domains of integrin beta subunits play a critical role in transducing the extracellular ligand-binding information into specific intracellular signaling events.


Assuntos
Integrina beta1/química , Integrina beta1/metabolismo , Integrina beta3/química , Integrina beta3/metabolismo , Transdução de Sinais , Proteínas rho de Ligação ao GTP/metabolismo , Actinas/metabolismo , Animais , Células CHO , Adesão Celular , Tamanho Celular , Cricetinae , Fibrinogênio/metabolismo , Fibronectinas/metabolismo , Humanos , Proteínas Quinases JNK Ativadas por Mitógeno , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Fosfatidilinositol 3-Quinases/metabolismo , Estrutura Terciária de Proteína , Fatores de Tempo , Transfecção , Proteínas rac de Ligação ao GTP/metabolismo
9.
J Biol Chem ; 277(20): 17804-10, 2002 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-11882657

RESUMO

ADAMs (a disintegrin and metalloproteases) are members of the metzincin superfamily of metalloproteases. Among integrins binding to disintegrin domains of ADAMs are alpha(9)beta(1) and alpha(v)beta(3), and they bind in an RGD-independent and an RGD-dependent manner, respectively. Human ADAM15 is the only ADAM with the RGD motif in the disintegrin domain. Thus, both integrin alpha(9)beta(1) and alpha(v)beta(3) recognize the ADAM15 disintegrin domain. We determined how these integrins recognize the ADAM15 disintegrin domain by mutational analysis. We found that the Arg(481) and the Asp-Leu-Pro-Glu-Phe residues (residues 488-492) were critical for alpha(9)beta(1) binding, but the RGD motif (residues 484-486) was not. In contrast, the RGD motif was critical for alpha(v)beta(3) binding, but the other residues flanking the RGD motif were not. As the RX(6)DLPEF alpha(9)beta(1) recognition motif (residues 481-492) is conserved among ADAMs, except for ADAM10 and 17, we hypothesized that alpha(9)beta(1) may recognize disintegrin domains in all ADAMs except ADAM10 and 17. Indeed we found that alpha(9)beta(1) bound avidly to the disintegrin domains of ADAM1, 2, 3, and 9 but not to the disintegrin domains of ADAM10 and 17. As several ADAMs have been implicated in sperm-oocyte interaction, we tested whether the functional classification of ADAMs, based on specificity for integrin alpha(9)beta(1), applies to sperm-egg binding. We found that the ADAM2 and 15 disintegrin domains bound to oocytes, but the ADAM17 disintegrin domain did not. Furthermore, the ADAM2 and 15 disintegrin domains effectively blocked binding of sperm to oocytes, but the ADAM17 disintegrin domain did not. These results suggest that oocytes and alpha(9)beta(1) have similar binding specificities for ADAMs and that alpha(9)beta(1), or a receptor with similar specificity, may be involved in sperm-egg interaction during fertilization. As alpha(9)beta(1) is a receptor for many ADAM disintegrins and alpha(9)beta(1) and ADAMs are widely expressed, alpha(9)beta(1)-ADAM interaction may be of a broad biological importance.


Assuntos
Sequência Conservada , Desintegrinas/metabolismo , Integrinas/metabolismo , Proteínas de Membrana/metabolismo , Metaloendopeptidases/metabolismo , Receptores de Vitronectina/metabolismo , Proteínas ADAM , Sequência de Aminoácidos , Animais , Arginina/metabolismo , Células CHO , Cricetinae , Feminino , Humanos , Proteínas de Membrana/classificação , Metaloendopeptidases/classificação , Camundongos , Modelos Moleculares , Dados de Sequência Molecular , Mutação Puntual , Interações Espermatozoide-Óvulo/fisiologia , Relação Estrutura-Atividade
10.
J Immunol ; 168(5): 2296-301, 2002 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-11859118

RESUMO

The alpha(L) I (inserted or interactive) domain of integrin alpha(L)beta(2) undergoes conformational changes upon activation. Recent studies show that the isolated, activated alpha(L) I domain is sufficient for strong ligand binding, suggesting the beta(2) subunit to be only indirectly involved. It has been unclear whether the activity of the alpha(L) I domain is regulated by the beta(2) subunit. In this study, we demonstrate that swapping the disulfide-linked CPNKEKEC sequence (residues 169-176) in the beta(2) I domain with a corresponding beta(3) sequence, or mutating Lys(174) to Thr, constitutively activates alpha(L)beta(2) binding to ICAM-1. These mutants do not require Mn(2+) for ICAM-1 binding and are insensitive to the inhibitory effect of Ca(2+). We have also localized a component of the mAb 24 epitope (a reporter of beta(2) integrin activation) in the CPNKEKEC sequence. Glu(173) and Glu(175) of the beta(2) I domain are identified as critical for mAb 24 binding. Because the epitope is highly expressed upon beta(2) integrin activation, it is likely that the CPNKEKEC sequence is exposed or undergoes conformational changes upon activation. Deletion of the alpha(L) I domain did not eliminate the mAb 24 epitope. This confirms that the alpha(L) I domain is not critical for mAb 24 binding, and indicates that mAb 24 detects a change expressed in part in the beta(2) subunit I domain. These results suggest that the CPNKEKEC sequence of the beta(2) I domain is involved in regulating the alpha(L) I domain.


Assuntos
Antígenos CD18/química , Antígeno-1 Associado à Função Linfocitária/química , Antígeno-1 Associado à Função Linfocitária/metabolismo , Sequência de Aminoácidos , Animais , Anticorpos Monoclonais/imunologia , Antígenos CD18/genética , Antígenos CD18/imunologia , Antígenos CD18/metabolismo , Células CHO , Adesão Celular , Sequência Conservada , Cricetinae , Dissulfetos/química , Epitopos/imunologia , Molécula 1 de Adesão Intercelular/metabolismo , Dados de Sequência Molecular , Mutação , Estrutura Terciária de Proteína , Alinhamento de Sequência
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