In humans, there are two skeletal muscle α‐actinins, encoded by ACTN2 and ACTN3, and the ACTN3 genotype is associated with human athletic performance. Remarkably, approximately 1 billion people worldwide are deficient in α‐actinin‐3 due to the common ACTN3 R577X polymorphism. The α‐actinins are an ancient family of actin‐binding proteins with structural, signalling and metabolic functions. The skeletal muscle α‐actinins diverged ∼250–300 million years ago, and ACTN3 has since developed restricted expression in fast muscle fibres. Despite ACTN2 and ACTN3 retaining (...) considerable sequence similarity, it is likely that following duplication there was a divergence in function explaining why α‐actinin‐2 cannot completely compensate for the absence of α‐actinin‐3. This paper focuses on the role of skeletal muscle α‐actinins, and how possible changes in functions between these duplicates fit in the context of gene duplication paradigms. (shrink)

The α‐actinins are an ancient family of actin‐binding proteins that play structural and regulatory roles in cytoskeletal organisation and muscle contraction. α‐actinin‐3 is the most‐highly specialised of the four mammalian α‐actinins, with its expression restricted largely to fast glycolytic fibres in skeletal muscle. Intriguingly, a significant proportion (∼18%) of the human population is totally deficient in α‐actinin‐3 due to homozygosity for a premature stop codon polymorphism (R577X) in the ACTN3 gene. Recent work in our laboratory has revealed a (...) strong association between R577X genotype and performance in a variety of athletic endeavours. We are currently exploring the function and evolutionary history of the ACTN3 gene and other α‐actinin family members. The α‐actinin family provides a fascinating case study in molecular evolution, illustrating phenomena such as functional redundancy in duplicate genes, the evolution of protein function, and the action of natural selection during recent human evolution. BioEssays 26:786–795, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

We now know that the evolution of multidomain proteins has frequently involved genetic duplication events. These, however, are sometimes difficult to trace because of low sequence similarity between duplicated segments. Spectrin, the major component of the membrane skeleton that provides elasticity to the cell, contains tandemly repeated sequences of 106 amino acid residues. The same repeats are also present in α‐actinin, dystrophin and utrophin. Sequence alignments and phylogenetic trees of these domains allow us to interpret the evolutionary relationship between (...) these proteins, concluding that spectrin evolved from α‐actinin by an elongation process that included two duplications of a block of seven repeats. This analysis shows how a modular protein unit can be used in the evolution of large cytoskeletal structures. (shrink)

Zyxin is a low abundance phosphoprotein that is localized at sites of cell‐substratum adhesion in fibroblasts. Zyxin displays the architectural features of an intracellular signal transducer. The protein exhibits an extensive proline‐rich domain, a nuclear export signal and three copies of the LIM motif, a double zinc‐finger domain found in many proteins that play central roles in regulation of cell differentiation. Zyxin interacts with α‐actinin, members of the cysteine‐rich protein (CRP) family, proteins that display Src homology 3 (SH3) domains (...) and Ena/VASP family members. Zyxin and its partners have been implicated in the spatial control of actin filament assembly as well as in pathways important for cell differentiation. Based on its repertoire of binding partners and its behavior, zyxin may serve as a scaffold for the assembly of multimeric protein machines that function in the nucleus and at sites of cell adhesion. (shrink)

The actin crosslinking proteins exhibit marked diversity in size and shape and crosslink actin filaments in different ways. Amino acid sequence analysis of many of these proteins has provided clues to the origin of their diversity. Spectrin, α‐actinin, ABP‐120, ABP‐280, fimbrin, and dystrophin share a homologous sequence segment that is implicated as the common actin binding domain. The remainder of each protein consists of repetitive and non‐repetitive sequence segments that have been shuffled and multiplied in evolution to produce a (...) variety of proteins that are related in function and in composition, but that differ significantly in structure. (shrink)

This article reviews and discusses emerging evidence suggesting an evolutionarily‐conserved connection between injury‐associated exposure of cytoskeletal proteins and the induction of tolerance to infection, repair of tissue damage and restoration of homeostasis. While differences exist between vertebrates and invertebrates with respect to the receptor(s), cell types, and effector mechanisms involved, the response to exposed cytoskeletal proteins appears to be protective and to rely on a conserved signaling cassette involving Src family kinases, the nonreceptor tyrosine kinase Syk, and tyrosine phosphatases. A (...) case is made for research programs that integrate different model organisms in order to increase the understanding of this putative response to tissue damage. (shrink)