The actin gene family: function follows isoform

Abstract

Although actin is often thought of as a single protein, in mammals it actually consists of six different isoforms encoded by separate genes. Each isoform is remarkably similar to every other isoform, with only slight variations in amino acid sequence. Nevertheless, recent work indicates that actin isoforms carry out unique cellular functions. Here, we review evidence drawn from localization studies, mouse models, and biochemical characterization to suggest a model for how in vivo mixing of actin isoforms may influence cytoskeletal function in cells.

Fig. 1. Actin-isoform sequence differences

A: Alignment of the N-terminal ends of the six mammalian actin isoforms. B: Amino acid differences mapped onto F-actin structure. The residues in red exhibit the most variability within and between muscle and cytoplasmic isoforms. Blue residues primarily vary between cytoplasmic and muscle isoforms. Yellow varies between β_cyto-actin and γ_cyto-actin while green indicates substitutions between different muscle isoforms. The F-actin structure is approximate and based on the work of Oda et al. [PDB 2ZWH, Oda et al., 2009].