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Updated: Sep 9, 2025

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
A Methionine-Rich Repeat Forms a Spiral Conformation That Guides Aragonite Nanofiber Organization in Molluscan
Kei Futagawa1, Haruki Meguro1, Koji Nagata1
1Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Abstract:
The hinge ligament of Pinctadafucata contains aragonite nanofibers embedded in a dense organic matrix primarily composed of ligament methionine (Met)-rich protein (LMP). LMP features a low-complexity region with 30 repeats of the Met-Met-Met-lysine-proline-aspartic acid (MMMKPD) sequence; however, its structural and functional roles remain unclear. Using synthetic peptides and solution nuclear magnetic resonance with dispersive aragonite particles, we observed that the MMMKPD repeat formed a unique spiral conformation distinct from canonical secondary structures, which was supported by AlphaFold predictions. This structure is stabilized by Met-driven hydrophobic interactions and facilitates the electrostatic alignment of the charged side chains for mineral binding. The spiral structure may represent a previously unrecognized structural motif adapted to mechanically dynamic or high-pressure environments, such as hinge ligaments. Our findings suggest a structural mechanism through which LMP directs aragonite nanofiber formation in molluscan biominerals.
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