second calponin homology (CH) domain found in the beta-I spectrin-like subfamily
The beta-I spectrin-like family includes beta-I, -II, -III and -IV spectrins. Spectrin is an actin crosslinking and molecular scaffold protein that links the plasma membrane to the actin cytoskeleton, and functions in the determination of cell shape, arrangement of transmembrane proteins, and organization of organelles. It is composed of two antiparallel dimers of alpha- and beta- subunits. Beta-I spectrin, also called spectrin beta chain, erythrocytic (SPTB), may be involved in anaemia pathogenesis. Beta-II spectrin, also called spectrin beta chain, non-erythrocytic 1 (SPTBN1), or fodrin beta chain, is a component of fodrin, which is the general spectrin-like protein that seems to be involved in secretion. Fodrin interacts with calmodulin in a calcium-dependent manner and is thus a candidate for the calcium-dependent movement of the cytoskeleton at the membrane. Beta-III spectrin, also called spectrin beta chain, non-erythrocytic 2 (SPTBN2), or spinocerebellar ataxia 5 protein (SCA5), may play a crucial role as a longer actin-membrane cross-linker or fulfill the need for greater extensible flexibility than can be provided by the other smaller conventional spectrins. Beta-IV spectrin is also called spectrin, non-erythroid beta chain 3 (SPTBN3) or spectrin beta chain, non-erythrocytic 4 (SPTBN4). Its mutation associates with congenital myopathy, neuropathy, and central deafness. Members of this subfamily contain two copies of the CH domain. This model corresponds to the second CH domain. CH domains are actin filament (F-actin) binding motifs.
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