Alternative titles; symbolsACTIN-RELATED PROTEIN 2/3 COMPLEX, 20-KD SUBUNIT; ARC20p20-ARCHGNC Approved Gene Symbol: ARPC4Cytogenetic location: 3p25.3 Genomic...
Alternative titles; symbols
HGNC Approved Gene Symbol: ARPC4
Cytogenetic location: 3p25.3 Genomic coordinates (GRCh38): 3:9,792,517-9,807,100 (from NCBI)
The Arp2/3 protein complex has been implicated in the control of actin polymerization in cells. The human complex consists of 7 subunits: the actin-related proteins ARP2 (ACTR2; 604221) and ARP3 (ACTR3; 604222), ARC41 (ARPC1B; 604223), ARC34 (ARPC2; 604224), ARC21 (ARPC3; 604225), ARC20 (ARPC4), and ARC16 (ARPC5; 604227). See ACTR2 for additional information about the Arp2/3 complex.
▼ Cloning and Expression
By searching an EST database with peptide sequences from the 7 subunits of the human ARP2/3 complex, Welch et al. (1997) identified full-length human cDNAs encoding each subunit. The ARC20 cDNA encodes a deduced 168-amino acid protein that is 68% and 67% identical to its homologs in S. pombe and S. cerevisiae, respectively.
Machesky et al. (1997) purified the ARP2/3 complex from human neutrophils and sequenced peptides from each of the subunits.
▼ Gene Function
Volkmann et al. (2001) performed electron cryomicroscopy and 3-dimensional reconstruction of Acanthamoeba castellanii and S. cerevisiae Arp2/3 complexes bound to the WASP (301000) carboxy-terminal domain. Asymmetric, oblate ellipsoids were revealed. Image analysis of actin branches indicated that the complex binds the side of the mother filament, and ARP2 and ARP3 are the first 2 subunits of the daughter filament. Comparison to the actin-free WASP-activated complexes suggests that branch initiation involves large-scale structural rearrangements within ARP2/3.
▼ Biochemical Features
Robinson et al. (2001) determined the crystal structure of bovine ARP2/3 complex at 2.0-angstrom resolution. ARP2 and ARP3 are folded like actin, with distinctive surface features. Subunits ARPC2 and ARPC4 in the core of the complex associate through long carboxy-terminal alpha helices and have similarly folded amino-terminal alpha/beta domains. ARPC1 is a 7-blade beta propeller with an insertion that may associate with the side of an actin filament. ARPC3 and ARPC5 are globular alpha-helical subunits. Robinson et al. (2001) predicted that WASP/SCAR proteins activate ARP2/3 complex by bringing ARP2 into proximity with ARP3 for nucleation of a branch on the side of a preexisting actin filament.