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An alternative N-terminal fold of the intestine-specific annexin A13a induces dimerization and regulates membrane-binding.

McCulloch K.M., Yamakawa I., Shifrin D.A. Jr., McConnell R.E., Foegeding N.J., Singh P.K., Mao S., Tyska M.J., Iverson T.M.

Annexin proteins function as Ca2+-dependent regulators of membrane trafficking and repair that may also modulate membrane curvature. Here, using high-resolution confocal imaging, we report that the intestine-specific annexin A13 (ANX A13) localizes to the tips of intestinal microvilli and determined the crystal structure of the ANX A13a isoform to 2.6 Å resolution. The structure revealed that the N terminus exhibits an alternative fold that converts the first two helices and the associated helix-loop-helix motif into a continuous α-helix, as stabilized by a domain-swapped dimer. We also found that the dimer is present in solution and partially occludes the membrane-binding surfaces of annexin, suggesting that dimerization may function as a means for regulating membrane binding. Accordingly, as revealed by in vitro binding and cellular localization assays, ANX A13a variants that favor a monomeric state exhibited increased membrane association relative to variants that favor the dimeric form. Together, our findings support a mechanism for how the association of the ANX A13a isoform with the membrane is regulated.

J. Biol. Chem. 294:3454-3463(2019) [PubMed] [Europe PMC]

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