Practice question

Magnetotactic bacteria such as Magnetospirillum magneticum AMB-1 and gryphiswaldense biomineralize magnetic nanoparticles within lipid vesicles called magnetosomes to navigate chemical gradients in stratified water columns. Cytoskeletal protein MamK actin homolog is essential for organizing magnetosomes into linear chain maximizing dipole moment for efficient orientation. MamK polymerizes ATP dependently into filaments extending along cell long axis, forms scaffold similar MreB but dedicated. Adaptor protein MamJ interacts with magnetosome membrane proteins MamY and MamK linking vesicles to filament, ensuring alignment at midcell near positive curvature and preventing agglomeration. Without MamK, magnetosomes dispersed clusters reducing magnetic orientation efficiency, cells unable to perform efficient magnetotaxis, chain fragmented after division. MamK dynamic polymerization also controls chain segmentation during division ensuring equal inheritance to daughters. Unlike plasmid segregation protein ParM requiring dynamic instability pushing apart or division FtsZ constricting, MamK specifically magnetosome positioning function. Additional proteins MamE protease, MamO scaffold regulate vesicle formation iron transport and magnetite nucleation precise control.