Calmodulin binds the N-terminus of the functional amyloid Orb2A inhibiting fibril formation.

The cytoplasmic polyadenylation element-binding protein Orb2 is a key regulator of long-term memory (LTM) in Drosophila. The N-terminus of the Orb2 isoform A is required for LTM and forms cross-ß fibrils on its own. However, this N-terminus is not part of the core found in ex vivo fibrils. We previously showed that besides forming cross-ß fibrils, the N-terminus of Orb2A binds anionic lipid membranes as an amphipathic helix. Here, we show that the Orb2A N-terminus can similarly interact with calcium activated calmodulin (CaM) and that this interaction prevents fibril formation. Because CaM is a known regulator of LTM, this interaction could potentially explain the regulatory role of Orb2A in LTM.

Droplet and fibril formation of the functional amyloid Orb2.

The functional amyloid Orb2 belongs to the cytoplasmic polyadenylation element binding (CPEB) protein family and plays an important role in long-term memory formation in Drosophila. The Orb2 domain structure combines RNA recognition motifs with low-complexity sequences similar to many RNA-binding proteins shown to form protein droplets via liquid-liquid phase separation (LLPS) in vivo and in vitro. This similarity suggests that Orb2 might also undergo LLPS. However, cellular Orb2 puncta have very little internal protein mobility, and Orb2 forms fibrils in Drosophila brains that are functionally active indicating that LLPS might not play a role for Orb2. In the present work, we reconcile these two views on Orb2 droplet formation. Using fluorescence microscopy, we show that soluble Orb2 can indeed phase separate into protein droplets. However, fluorescence recovery after photobleaching (FRAP) data shows that these droplets have either no or only an extremely short-lived liquid phase and appear maturated right after formation. Orb2 fragments that lack the C-terminal RNA-binding domain (RBD) form fibrils out of these droplets. Solid-state NMR shows that these fibrils have well-ordered static domains in addition to the Gln/His-rich fibril core. Further, we find that full-length Orb2B, which is by far the major component of Orb2 fibrils in vivo, does not transition into fibrils but remains in the droplet phase. Together, our data suggest that phase separation might play a role in initiating the formation of functional Orb2 fibrils.

Mexican Concensus of Multiple Myeloma.

To identify this increasingly common pathology, known as multiple myeloma (MM), it is necessary to refer to the specific factors that characterize it; to this end, the classic criteria known as CRAB (hyperkalemia, renal failure, anemia, and lytic lesions) are available, in which renal failure is one of the most frequent complications. Recently, three indisputable biomarkers have been described for the diagnostic support for MM, which are: more than 10% of clonal plasma cells in bone marrow or, a biopsy that corroborates the presence of a plasmacytoma, light chain ratio ≥ 100 mg/dL and more than one focal lesion on magnetic resonance imaging. A differential diagnosis for plasma cell leukemia, solitary bone plasmacytoma, and extramedullary plasmacytoma should always be considered. Being this an incurable disease, a lot of research has been done regarding its therapeutic management, whose main objective is the disappearance of plasma cells and the patient clinical improvement. Melphalan was the first drug that showed a benefit in 1958 and afterward, with the addition of a steroid as a second drug, it was possible to improve response rates. Subsequently, different molecules were studied, forming multiple combinations, and achieving better rates of overall survival and progression-free survival. Years later, with the arrival of proteasome inhibitors such as bortezomib, and immunomodulators such as thalidomide and lenalidomide, an important turnaround in the disease has been seen, as deeper responses, more prolonged remissions, and improvement in the quality of life of patients have been achieved. This consensus has the purpose of integrating a group of Mexican specialists and promoting the updating of this pathology.

Para identificar una patología cada vez más común, conocida como mieloma múltiple, es necesario hacer alusión de los factores específicos que la caracterizan. Para ello existen los clásicos criterios conocidos como CRAB (hipercalcemia, insuficiencia renal, anemia y lesiones líticas), siendo la insuficiencia renal una de sus complicaciones más frecuentes. Recientemente se han descrito tres biomarcadores indiscutibles para el apoyo diagnóstico del mieloma múltiple, que son: más del 10% de células plasmáticas clonales en medula ósea o biopsia que corrobora la presencia de un plasmocitoma, relación de cadenas ligeras ≥ 100 mg/dl y más de una lesión focal en resonancia magnética. Se debe tomar siempre en cuenta el diagnóstico diferencial con leucemia de células plasmáticas, plasmocitoma óseo solitario y plasmocitoma extramedular. Al ser una enfermedad incurable, se ha investigado mucho en cuanto al manejo terapéutico, el cual tiene como objetivo principal la desaparición de las células plasmáticas y la mejoría clínica del paciente. El primer fármaco que demostró algún beneficio fue el melfalán en el año 1958 y posteriormente al adicionar un esteroide como segundo fármaco se logró mejorar las tasas de respuesta. Después se fueron estudiando diferentes moléculas, con las que se han realizado múltiples combinaciones, alcanzando mejores tasas de supervivencia global y supervivencia libre de progresión. Años más tarde, con la llegada de los inhibidores de proteosoma como el bortezomib, así como de los agentes inmunomoduladores como la talidomida y la lenalidomida, se presenta un giro importante en la enfermedad, ya que se logran respuestas más profundas, periodo de remisiones más prolongadas y mejoría en la calidad de vida de los pacientes. Este consenso tiene la finalidad de integrar a un grupo de especialistas mexicanos y promover la actualización de esta patología.

Participant-Centered Strategies for Overcoming Barriers to Biospecimen Collection among Spanish-Speaking Latina Breast Cancer Survivors.

BACKGROUND: Latinos are underrepresented in biomedical research, particularly biomarker research, yet they constitute the nation's largest ethnic/racial minority. Optimal methods for obtaining biospecimens for biomarker research among Latinos need to be identified. To minimize barriers and enhance participation, this study developed and tested tailored strategies for collecting biomarkers of chronic stress and premature aging among Spanish-speaking Latina breast cancer survivors. METHODS: This study used a community-based participatory approach and selected hair and saliva as noninvasive biospecimens to assess telomere length, the cortisol awakening response (CAR), and hair cortisol concentration. We developed bilingual multimedia instructional materials, and community health workers assisted in collections. Telephone surveys assessed willingness to participate in future studies, barriers to sample collection, and recommendations for improving the strategies. RESULTS: A total of 103 participants were recruited over 18 months from two rural sites in California, and 88 were retained at 6-month follow-up. At baseline, rates of donating salivary DNA for telomere length measurement, saliva for CAR analysis, and hair for cortisol concentration were 98%, 89%, and 52%, respectively. At follow-up, rates were 83%, 76%, and 55%, respectively. The majority of participants reported being very willing to provide hair (72%) or saliva (74%) for future studies. CONCLUSIONS: Our results support the feasibility of including minorities in biomedical research. We report excellent rates of saliva collection when community partners are engaged in the process, and when patient-centered and culturally tailored recruitment methods are implemented. IMPACT: The development of methods to facilitate the inclusion of minorities in biomedical research is critical to eliminate racial/ethnic health disparities.

Dynamics of the Proline-Rich C-Terminus of Huntingtin Exon-1 Fibrils.

Intrinsically disordered protein domains not only are found in soluble proteins but also can be part of large protein complexes or protein aggregates. For example, several amyloid fibrils have intrinsically disordered domains framing a rigid ß-sheet-rich core. These disordered domains can often be observed using solution NMR methods in combination with modest magic angle spinning and without perdeuteration. But how can these regions be detected using solution NMR methods when they are part of a fibril that is not tumbling isotropically in solution? Here we addressed this question by investigating the dynamic C-terminus of huntingtin exon-1 (HTTex1) fibrils that are important in Huntington's disease. We assigned the most dynamic regions of the C-terminus of three HTTex1 variants. On the basis of this assignment, we measured site-specific secondary chemical shifts, peak intensities, and R1, R'2, and R1ρ 15N relaxation rates. In addition, we determined the residual 1H-15N dipolar couplings of this region. Our results show that the dipolar couplings are averaged to a very high degree, resulting in an order parameter that is essentially zero. Together, our data show that the C-terminus of HTTex1 is intrinsically disordered and undergoes motions in the high picosecond to low nanosecond range.

Metal Binding Properties of the N-Terminus of the Functional Amyloid Orb2.

The cytoplasmic polyadenylation element binding protein (CPEB) homologue Orb2 is a functional amyloid that plays a key regulatory role for long-term memory in Drosophila. Orb2 has a glutamine, histidine-rich (Q/H-rich) domain that resembles the Q/H-rich, metal binding domain of the Hpn-like protein (Hpnl) found in Helicobacter pylori. In the present study, we used chromatography and isothermal titration calorimetry (ITC) to show that the Q/H-rich domain of Orb2 binds Ni2+ and other transition metals ions with µM affinity. Using site directed mutagenesis, we show that several histidine residues are important for binding. In particular, the H61Y mutation, which was previously shown to affect the aggregation of Orb2 in cell culture, completely inhibited metal binding of Orb2. Finally, we used thioflavin T fluorescence and electron microscopy images to show that Ni2+ binding induces the aggregating of Orb2 into structures that are distinct from the amyloid fibrils formed in the absence of Ni2+. These data suggest that transition metal binding might be important for the function of Orb2 and potentially long-term memory in Drosophila.

The Functional Amyloid Orb2A Binds to Lipid Membranes.

Lipid membranes interact with and influence the aggregation of many amyloid-forming proteins. Orb2 is a cytoplasmic polyadenylation element-binding protein homolog in Drosophila melanogaster that forms functional amyloids necessary for long-term memory. One isoform, Orb2A, has a unique N-terminus that has been shown to be important for the formation of amyloid-like aggregates and long-term memory in vivo. Orb2A is also found enriched in the synaptic membrane fraction. Our sequence and hydropathy analysis suggests that it can form an amphipathic helix, which is ideal for lipid membrane interaction. We used circular dichroism and site-directed spin labeling coupled with electron paramagnetic resonance to test the first 88 amino acids of Orb2A for lipid interaction. We show that Orb2A1-88 interacts with anionic lipid membranes using an amphipathic helix at its unique N-terminus. This interaction depends on the charge of the lipid membrane and the degree of membrane curvature. We used transmission electron microscopy and electron paramagnetic resonance to show that the presence of anionic small unilamellar vesicles inhibits amyloid fibril formation by Orb2A. This inhibition by anionic membranes could be a potential mechanism regulating Orb2A amyloid formation in vivo.

Identification and Structural Characterization of the N-terminal Amyloid Core of Orb2 isoform A.

Orb2 is a functional amyloid that plays a key role in Drosophila long-term memory formation. Orb2 has two isoforms that differ in their N-termini. The N-terminus of the A isoform (Orb2A) that precedes its Q-rich prion-like domain has been shown to be important for Orb2 aggregation and long-term memory. However, besides the fact that it forms fibrillar aggregates, structural information of Orb2 is largely absent. To understand the importance of the N-terminus of Orb2A and its relation to the fibril core, we recorded solid-state NMR and EPR data on fibrils formed by the first 88 residues of Orb2A (Orb2A88). These data show that the N-terminus of Orb2A not only promotes the formation of fibrils, but also forms the fibril core of Orb2A88. This fibril core has an in-register parallel ß-sheet structure and does not include the Q-rich, prion-like domain of Orb2. The Q-rich domain is part of the unstructured region, which becomes increasingly dynamic towards the C-terminus.