Structural highlights
FunctionPublication Abstract from PubMedSca2 (surface cell antigen 2) is the only bacterial protein known to promote both actin filament nucleation and profilin-dependent elongation, mimicking eukaryotic formins to assemble actin comet tails for Rickettsia motility. We show that Sca2's functional mimicry of formins is achieved through a unique mechanism. Unlike formins, Sca2 is monomeric, but has N- and C-terminal repeat domains (NRD and CRD) that interact with each other for processive barbed-end elongation. The crystal structure of NRD reveals a previously undescribed fold, consisting of helix-loop-helix repeats arranged into an overall crescent shape. CRD is predicted to share this fold and might form together with NRD, a doughnut-shaped formin-like structure. In between NRD and CRD, proline-rich sequences mediate the incorporation of profilin-actin for elongation, and WASP-homology 2 (WH2) domains recruit actin monomers for nucleation. Sca2's alpha-helical fold is unusual among Gram-negative autotransporters, which overwhelmingly fold as beta-solenoids. Rickettsia has therefore "rediscovered" formin-like actin nucleation and elongation. Rickettsia Sca2 has evolved formin-like activity through a different molecular mechanism.,Madasu Y, Suarez C, Kast DJ, Kovar DR, Dominguez R Proc Natl Acad Sci U S A. 2013 Jul 16;110(29):E2677-86. doi:, 10.1073/pnas.1307235110. Epub 2013 Jul 1. PMID:23818602[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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