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Functional consequences of the oligomeric assembly of proteorhodopsin.

ABSTRACT: The plasma membrane is the crucial interface between the cell and its exterior, packed with embedded proteins experiencing simultaneous protein-protein and protein-membrane interactions. A prominent example of cell membrane complexity is the assembly of transmembrane proteins into oligomeric structures, with potential functional consequences that are not well understood. From the study of proteorhodopsin (PR), a prototypical seven-transmembrane light-driven bacterial proton pump, we find evidence that the inter-protein interaction modulated by self-association yields functional changes observable from the protein interior. We also demonstrate that the oligomer is likely a physiologically relevant form of PR, as crosslinking of recombinantly expressed PR reveals an oligomeric population within the Escherichia coli membrane (putatively hexameric). Upon chromatographic isolation of oligomeric and monomeric PR in surfactant micelles, the oligomer exhibits distinctly different optical absorption properties from monomeric PR, as reflected in a prominent decrease in the pKa of the primary proton acceptor residue (D97) and slowing of the light-driven conformational change. These functional effects are predominantly determined by specific PR-PR contacts over nonspecific surfactant interactions. Interestingly, varying the surfactant type alters the population of oligomeric states and the proximity of proteins within an oligomer, as determined by sparse electron paramagnetic resonance distance measurements. Nevertheless, the dynamic surfactant environment retains the key function-tuning property exerted by oligomeric contacts. A potentially general design principle for transmembrane protein function emerges from this work, one that hinges on specific oligomeric contacts that can be modulated by protein expression or membrane composition.

SUBMITTER: Hussain S

PROVIDER: S-EPMC4374980 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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Functional consequences of the oligomeric assembly of proteorhodopsin.

Hussain Sunyia S Kinnebrew Maia M Schonenbach Nicole S NS Aye Emily E Han Songi S

Journal of molecular biology 20150115 6 Pt B

The plasma membrane is the crucial interface between the cell and its exterior, packed with embedded proteins experiencing simultaneous protein-protein and protein-membrane interactions. A prominent example of cell membrane complexity is the assembly of transmembrane proteins into oligomeric structures, with potential functional consequences that are not well understood. From the study of proteorhodopsin (PR), a prototypical seven-transmembrane light-driven bacterial proton pump, we find evidenc ...[more]

PMID: 25597999

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Project description:gp41, one of the baculovirus core genes, encodes the only recognized tegument (O-glycosylated) protein of the occlusion-derived virion (ODV) phenotype so far. A previous study using a temperature-sensitive Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) mutant showed that GP41 plays a crucial role in budded virion (BV) formation. However, the precise function of GP41 in the baculovirus replication cycle remains unclear. In this study, AcMNPV GP41 was found to accumulate around the ring zone (RZ) region within the infected nucleus and finally assembled into both BVs and ODVs. Deletion of gp41 from the AcMNPV genome showed that BVs were no longer formed and ODVs were no longer assembled, suggesting the essential role of this gene in baculovirus virion morphogenesis. In infected cells, besides the 42-kDa monomers, dimers and trimers were detected under nonreducing conditions, whereas only trimeric GP41 forms were selectively incorporated into BVs or ODVs. Mutations of all five cysteines in GP41 individually had minor effects on GP41 oligomer formation, albeit certain mutations impaired infectious BV production, suggesting flexibility in the intermolecular disulfide bonding. Single mutations of key leucines within two predicted leucine zipper-like motifs did not interfere with GP41 oligomerization or BV and ODV formation, but double leucine mutations completely blocked oligomerization of GP41 and progeny BV production. In the latter case, the usual subcellular localization, especially RZ accumulation, of GP41 was abolished. The above findings clearly point out a close correlation between GP41 oligomerization and function and therefore highlight the oligomeric state as the functional form of GP41 in the baculovirus replication cycle.IMPORTANCE The tegument, which is sandwiched between the nucleocapsid and the virion envelope, is an important substructure of many enveloped viruses. It is composed of one or more proteins that have important functions during virus entry, replication, assembly, and egress. Unlike another large DNA virus (herpesvirus) that encodes an extensive set of tegument components, baculoviruses very likely exploit the major tegument protein, GP41, to execute functions in baculovirus virion morphogenesis and assembly. However, the function of this O-glycosylated baculovirus tegument protein remains largely unknown. In this study, we identified trimers as the functional structure of GP41 in baculovirus virion morphogenesis and showed that both disulfide bridging and protein-protein interactions via the two leucine zipper-like domains are involved in the formation of different oligomeric states. This study advances our understanding of the unique viral tegument protein GP41 participating in the life cycle of baculoviruses.

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Functional consequences of the oligomeric assembly of proteorhodopsin.

Publications

Functional consequences of the oligomeric assembly of proteorhodopsin.

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