MamK filament

cellstructuremech:mamk_filament · Cytoskeleton · Filament · Proposed

An actin-like bacterial cytoskeletal filament assembled from MamK proteins that runs alongside magnetosomes in magnetotactic bacteria and helps organize the organelles into chains. [DOI:10.1126/science.1123231]

Synonyms: MamK actin-like filament; magnetosome-associated MamK filament

Part of: GO:0005856 — cytoskeleton (no local record)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
MamK actin homolog	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	mamK		ESSENTIAL	Bacterial actin homolog that polymerizes into the cytoskeletal filament associated with magnetosome chains. `DOI:10.1126/science.1123231` Komeili et al. 2006 identified MamK as the actin-like protein organizing magnetosomes in Paramagnetospirillum magneticum AMB-1. `DOI:10.1002/pro.2979` Bergeron et al. 2017 reported a cryo-EM structure of a polymerized MamK filament.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

MamK actin homolog

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q2W8Q6`	Actin-like protein MamK	mamK	Paramagnetospirillum magneticum AMB-1 (`NCBITaxon:342108`)	REVIEWED
Role and evidence (1 reference) Reviewed AMB-1 MamK accession aligned by RCSB to the polymer entity in the PDB:5JYG MamK filament cryo-EM model. `PDB:5JYG` RCSB PDB entry 5JYG is a 6.5 A cryo-EM structure of the Paramagnetospirillum magneticum AMB-1 MamK filament associated with EMDB map EMD-8180.
`UniProtKB:Q6NE59`	Actin-like protein MamK	mamK	Magnetospirillum gryphiswaldense MSR-1 (`NCBITaxon:431944`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene mamK in Magnetospirillum gryphiswaldense MSR-1. `PMID:20487281` Katzmann et al. 2010 studied the effect of mamK loss on magnetosome formation and chain assembly in Magnetospirillum gryphiswaldense.

Taxonomic distribution

NCBITaxon:2 Bacteria — RARE: MamK filaments are restricted to magnetotactic bacterial lineages; the directly studied strains are magnetospirilla. [DOI:10.1038/nrmicro.2016.99]

Canonical examples

NCBITaxon:342108 Paramagnetospirillum magneticum AMB-1 — Model strain in which MamK was tied to magnetosome-chain organization and source of the MamK cryo-EM filament model PDB:5JYG. [DOI:10.1126/science.1123231]
NCBITaxon:431944 Magnetospirillum gryphiswaldense MSR-1 — Model strain used to test MamK function in magnetosome chain assembly. [PMID:20487281]

Functions

magnetosome chain organization — Organizes magnetosome organelles into an intracellular chain aligned with the cell axis.
- DOI:10.1126/science.1123231 Komeili et al. 2006 showed that MamK is required for proper subcellular organization of magnetosome chains in AMB-1.
- PMID:20487281 Katzmann et al. 2010 connected loss of MamK with magnetosome formation and chain-assembly defects in MSR-1.

Mechanism graphs

MamK filaments organize magnetosome chains (FUNCTION)

MamK proteins polymerize into cytoskeletal filaments that run along magnetosome chains and help maintain the organelles in a linear arrangement.

Subject	Predicate	Object	Evidence
MamK actin homolog	polymerizes into	MamK filament	`DOI:10.1002/pro.2979` Bergeron et al. 2017 solved the polymerized MamK filament by cryo-EM.
MamK filament	organizes	magnetosome	`DOI:10.1126/science.1123231` Komeili et al. 2006 used electron cryotomography to connect cytoskeletal filaments and MamK with magnetosome organization in AMB-1 cells.
MamK filament	aligns	magnetosome chain	`DOI:10.1038/nrmicro.2016.99` Uebe and Schuler 2016 describe MamK/MamJ-dependent magnetosome chain organization.

Discussions

CURATION_TODO (OPEN): Resolve an exact source-neutral InterPro, Pfam, or NCBIfam identifier for filament-forming magnetosome MamK proteins. This record represents the magnetosome-associated MamK filament without asserting that a broader bacterial actin, MreB/MamK-like, or domain-level accession exactly denotes MamK filament subunits.

Evidence

DOI:10.1126/science.1123231 Komeili, Li, Newman and Jensen 2006, Magnetosomes Are Cell Membrane Invaginations Organized by the Actin-Like Protein MamK, Science.
DOI:10.1002/pro.2979 Bergeron, Hutto, Ozyamak et al. 2017, Structure of the magnetosome-associated actin-like MamK filament at subnanometer resolution, Protein Science.
PDB:5JYG RCSB PDB entry 5JYG is the atomic model for the 6.5 A MamK filament cryo-EM reconstruction from Paramagnetospirillum magneticum AMB-1.
EMDB:EMD-8180 EMDB entry EMD-8180 is the helical-reconstruction map paired with PDB:5JYG for the MamK filament.
DOI:10.1038/nrmicro.2016.99 Uebe and Schuler 2016 reviewed MamK/MamJ-dependent magnetosome chain organization in magnetotactic bacteria.
GO:0099513 — polymeric cytoskeletal fiber Broader polymeric cytoskeletal fiber class; this protein filament retains its specific local identity.
GO:0005856 — cytoskeleton The cytoskeletal framework contains this filament; the filament is part of it, not a type of the entire framework.

Curation history

2026-09-13T08:09:18Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-13T08:10:42Z codex · EXPANDED_RECORD — Added cytoskeleton parentage, MamK filament synonymy, a label-only MamK component with AMB-1 and MSR-1 UniProt examples, magnetotactic-bacterium scope, DOI/PDB/EMDB evidence, a nonmechanistic magnetosome-chain graph, and a MamK-family grounding TODO.
2026-09-13T08:15:28Z codex · REVIEW_MAMK_INTERPRO_SCOPE — Narrowed the MamK grounding note to the exact InterPro families reviewed for the AMB-1 and MSR-1 MamK examples.
2026-10-11T18:52:17Z codex · ADDRESS_SAVED_REVIEW — Addressed #2240: Corrected cytoskeletal fiber is-a and containing-framework parthood.

Source: data/structures/cytoskeleton/mamk_filament.yaml