The physical properties of supramolecular peptide assemblies: from building block association to technological applications

Bio-inspired nano-materials can be formed by the ordered assembly of elementary building blocks. These peptide nanostructures can be utilized in many applications in various fields ranging from energy storage devices to drug delivery agents.

β-Arrestin multimers: does a crowd help or hinder function?

In this issue of the Biochemical Journal, Xu et al. describe how they use a spot peptide array to identify a unique sequence within β-arrestin-2 that is required for both multimerization and ERK1/2 (extracellular-signal-related kinase 1/2) scaffolding. They provide evidence that dimers may serve as more than just ‘storage forms’ of β-arrestins, incapable of interacting with receptors but, rather, perhaps, adding to the specificity of G-protein-coupled-receptor signalling. They show that key charged residues within this dimerization interface of β-arrestin-2 block association with ERK1/2 and subsequent activation of ERK1/2 by β2-adrenergic receptors, while internalization is unaffected. They suggest that self-association may serve as a means of sheltering scaffolding sites on β-arrestins from specific binding partners to prevent constitutive activation of key signalling pathways. These studies enhance our understanding of how β-arrestins can juggle their roles as scaffolds of multiple pathways in response to diverse signals.

Neutralization of Human Papillomavirus with Monoclonal Antibodies Reveals Different Mechanisms of Inhibition

ABSTRACT The mechanisms of human papillomavirus (HPV) neutralization by antibodies are incompletely understood. We have used HPV16 pseudovirus infection of HaCaT cells to analyze how several neutralizing monoclonal antibodies (MAbs) generated against HPV16 L1 interfere with the process of keratinocyte infection. HPV16 capsids normally bind to both the cell surface and extracellular matrix (ECM) of HaCaT cells. Surprisingly, two strongly neutralizing MAbs, V5 and E70, did not prevent attachment of capsids to the cell surface. However, they did block association with the ECM and prevented internalization of cell surface-bound capsids. In contrast, MAb U4 prevented binding to the cell surface but not to the ECM. The epitope recognized by U4 was inaccessible when virions were bound to the cell surface but became accessible after endocytosis, presumably coinciding with receptor detachment. Treatment of capsids with heparin, which is known to interfere with binding to cell surface heparan sulfate proteoglycans (HSPGs), also resulted in HPV16 localization to the ECM. These results suggest that the U4 epitope on the intercapsomeric C-terminal arm is likely to encompass the critical HSPG interaction residues for HPV16, while the V5 and E70 epitopes at the apex of the capsomer overlap the ECM-binding sites. We conclude that neutralizing antibodies can inhibit HPV infection by multiple distinct mechanisms, and understanding these mechanisms can add insight to the HPV entry processes.

Plasma membrane Ca2+-ATPase (PMCA) translocates to filopodia during platelet activation

SummaryThe plasma membrane Ca2+-ATPase (PMCA) plays an essential role in maintaining low cytosolic Ca2+ in platelets. Recently we demonstrated that PMCA is recruited to the cytoskeleton by interacting with PDZ domains. In the present study we determined the subcellular localization of PMCA using immunofluorescence microscopy. In resting platelets PMCA was distributed over the entire plasma membrane. Upon activation with thrombin, PMCA was found in filopodia adjacent to the actin cytoskeleton. PMCA translocation to filopodia was prevented by a peptide containing the last 10 residues of PMCA4b, the predominate isoform of PMCA in platelets, which contains a known PDZ domain-binding motif and was previously shown to block association of PMCA with the cytoskeleton. Incorporation of the PMCA C-terminal peptide did not affect the rate or extent of platelet aggregation, but significantly enhanced the rate of clot retraction. These results show that PMCA association with the cytoskeleton during platelet activation results in translocation of this Ca2+-pump to filopodia and that this association may affect later stages of platelet activation. The consequence of PMCA translocation to filopodia is likely a reduction in the local concentration of free Ca2+ in these structures resulting in regulation of the rate of clot retraction.