Structural studies of phosphorylation-dependent interactions between the V2R receptor and arrestin-2

Arrestins recognize different receptor phosphorylation patterns and convert this information to selective arrestin functions to expand the functional diversity of the G protein-coupled receptor (GPCR) superfamilies. However, the principles governing arrestin-phospho-receptor interactions, as well as the contribution of each single phospho-interaction to selective arrestin structural and functional states, are undefined. Here, we determined the crystal structures of arrestin2 in complex with four different phosphopeptides derived from the vasopressin receptor-2 (V2R) C-tail. A comparison of these four crystal structures with previously solved Arrestin2 structures demonstrated that a single phospho-interaction change results in measurable conformational changes at remote sites in the complex. This conformational bias introduced by specific phosphorylation patterns was further inspected by FRET and 1H NMR spectrum analysis facilitated via genetic code expansion. Moreover, an interdependent phospho-binding mechanism of phospho-receptor-arrestin interactions between different phospho-interaction sites was unexpectedly revealed. Taken together, our results provide evidence showing that phospho-interaction changes at different arrestin sites can elicit changes in affinity and structural states at remote sites, which correlate with selective arrestin functions.

MreC and MreD balance the interaction between the elongasome proteins PBP2 and RodA

Rod-shape of most bacteria is maintained by the elongasome, which mediates the synthesis and insertion of peptidoglycan into the cylindrical part of the cell wall. The elongasome contains several essential proteins, such as RodA, PBP2, and the MreBCD proteins, but how its activities are regulated remains poorly understood. Using E. coli as a model system, we investigated the interactions between core elongasome proteins in vivo. Our results show that PBP2 and RodA form a complex mediated by their transmembrane and periplasmic parts and independent of their catalytic activity. MreC and MreD also interact directly with PBP2. MreC elicits a change in the interaction between PBP2 and RodA, which is suppressed by MreD. The cytoplasmic domain of PBP2 is required for this suppression. We hypothesize that the in vivo measured PBP2-RodA interaction change induced by MreC corresponds to the conformational change in PBP2 as observed in the MreC-PBP2 crystal structure, which was suggested to be the “on state” of PBP2. Our results indicate that the balance between MreC and MreD determines the activity of PBP2, which could open new strategies for antibiotic drug development.

Interaction, Change, and the Role of the Historical in Validation: The Case of L2 Dynamic Assessment

This article examines the implications of argument-based validity for the continued development of dynamic assessment (DA) research and practice. We propose that the move toward validation as a process of interpretation and evidence-based argument is commensurable with DA but that fundamental ontological differences with conventional approaches to measurement must be recognized. Following Ollman’s (2003) explication of dialectical thinking, and in particular the distinction between philosophies of external and internal relations, we submit that the standard view of abilities as discrete traits is untenable in DA. Instead, abilities must be understood in a manner that takes account of (a) available forms of mediation and (b) change that occurs over the course of DA. To illustrate how a process of validation might be undertaken in DA, we present findings from recent DA studies involving second language learners. Our discussion brings into focus both learner participation in DA interactions and score changes over time.

Increasing Student Interaction in Technical Writing Courses in Online Environments

This article examines how the levels of student interaction change through the use of small groups and moderators in online writing courses. The study examines three technical and professional online writing courses: one course that employs small groups and group moderators and two courses that have no small groups or moderators. The results of this study show that the amount of interaction between students in online writing courses increases dramatically by incorporating small groups and peer moderators.

Why we need to examine multiple social network sites

The hyper-concentration of research on mainstream social media sites like Facebook and Twitter comes at the cost of lesser emphasis on, if not the exclusion of, other platforms and practices. How might our conceptualizations of social media and social interaction change if we were to explore a wider range of systems to enrich our theorizing? This piece considers three examples of how looking beyond the usual suspects may broaden our understanding of how social media sites play into privacy management, identity work, and interpersonal relationships. I argue that our theorizing of social media and the practices that surround them gains strength from exploring varied sites of study.