RESUMO
Many members of the tumor necrosis factor receptor (TNFR) superfamily initiate intracellular signaling by recruiting TNFR-associated factors (TRAFs) through their cytoplasmic tails. TRAFs apparently recognize highly diverse receptor sequences. Crystal structures of the TRAF domain of human TRAF2 in complex with peptides from the TNFR family members CD40, CD30, Ox40, 4-1BB, and the EBV oncoprotein LMP1 revealed a conserved binding mode. A major TRAF2-binding consensus sequence, (P/S/A/T)x(Q/E)E, and a minor consensus motif, PxQxxD, can be defined from the structural analysis, which encompass all known TRAF2-binding sequences. The structural information provides a template for the further dissection of receptor binding specificity of TRAF2 and for the understanding of the complexity of TRAF-mediated signal transduction.
Assuntos
Proteínas/química , Receptores do Fator de Necrose Tumoral/química , Sequência de Aminoácidos , Antígenos CD , Sítios de Ligação , Antígenos CD40/química , Antígenos CD40/metabolismo , Sequência Consenso , Cristalografia por Raios X , Humanos , Antígeno Ki-1/química , Antígeno Ki-1/metabolismo , Modelos Moleculares , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Conformação Proteica , Proteínas/metabolismo , Receptores de Fator de Crescimento Neural/química , Receptores de Fator de Crescimento Neural/metabolismo , Receptores do Fator de Necrose Tumoral/metabolismo , Transdução de Sinais , Fator 2 Associado a Receptor de TNF , Membro 9 da Superfamília de Receptores de Fatores de Necrose Tumoral , Fator de Necrose Tumoral alfa/química , Fator de Necrose Tumoral alfa/metabolismo , Proteínas da Matriz Viral/química , Proteínas da Matriz Viral/metabolismoRESUMO
Pneumocystis carinii pneumonia (PcP) remains among the most prevalent opportunistic infections among AIDS patients. Currently, drugs used clinically for deep mycosis act by binding ergosterol or disrupting its biosynthesis. Although classified as a fungus, P. carinii lacks ergosterol. Instead, the pathogen synthesizes a number of distinct Delta7, 24-alkylsterols, despite the abundance of cholesterol, which it can scavenge from the lung alveolus. Thus, the pathogen-specific sterols appear vital for organism survival and proliferation. In the present study, high concentrations of a C32 sterol were found in human-derived P. carinii hominis. The definitive structural identities of two C-24 alkylated lanosterol compounds, previously not reported for rat-derived P. carinii carinii, were determined by using GLC, MS, and NMR spectroscopy together with the chemical syntheses of authentic standards. The C31 and C32 sterols were identified as euphorbol (24-methylenelanost-8-en-3beta-ol) and pneumocysterol [(24Z)-ethylidenelanost-8-en-3beta-ol], respectively. The identification of these and other 24-alkylsterols in P. carinii hominis suggests that (i) sterol C-24 methyltransferase activities are extraordinarily high in this organism, (ii) 24-alkylsterols are important components of the pathogen's membranes, because the addition of these side groups onto the sterol side chain requires substantial ATP equivalents, and (iii) the inefficacy of azole drugs against P. carinii can be explained by the ability of this organism to form 24-alkysterols before demethylation of the lanosterol nucleus. Because mammals cannot form 24-alkylsterols, their biosyntheses in P. carinii are attractive targets for the development of chemotherapeutic strategies against this opportunistic infection.
