MamK

MamK is a prokaryotic actin-like cytoskeletal protein encoded by the mamK gene within the magnetosome gene island of magnetotactic bacteria, most notably in Magnetospirillum species. As a member of the actin superfamily, MamK can polymerize into filamentous structures in an ATP-dependent manner, forming filaments that run through the cytoplasm.

In magnetotactic bacteria, the MamK filament acts as a scaffold for organizing magnetosome vesicles into linear chains. The connection between magnetosome membranes and the MamK filament is mediated by MamJ, a linker protein that binds to both the magnetosome surface and MamK. This MamK–MamJ system aligns magnetosomes along the cell’s longitudinal axis, positioning the magnetic crystals to optimize magnetic moment and navigation.

Genetic disruption of mamK disrupts chain organization: mutants often show scattered magnetosomes rather than a continuous chain, though some residual organization may persist in certain species. Filaments formed by MamK have been observed in several magnetotactic bacteria, and in vitro studies support actin-like polymerization dynamics, though the precise behavior can vary between species.

MamK is part of the broader magnetosome gene island and functions in concert with other magnetosome proteins such as MamA, MamB, and MamJ to coordinate chain assembly. The resulting magnetosome chain is considered important for efficient magnetotaxis, helping cells align with magnetic field lines and improve directional movement in aquatic environments. See also magnetosome, MamJ, and magnetotaxis.