Brush-border alpha-actinin? Comparison of two proteins of the microvillus core with alpha-actinin by two-dimensional peptide mapping.

Abstract

The bundle of filaments within the intestinal microvillus contains 4 major polypeptides in addition to actin: calmodulin, a 70 kdalton subunit and 2 polypeptides with molecular masses similar to that of the Z-line component alpha-actinin (95 and 105 kdaltons). Two-dimensional mapping of tryptic peptides indicates that alpha-actinins from chicken skeletal, cardiac and smooth muscle are apparently similar but not identical proteins and that skeletal alpha-actinin is more similar to the cardiac subunit than to the alpha-actinin from gizzard; the brush-border 95 and 105 kdalton subunits are apparently closely related to each other, but the smaller subunit is not a proteolytic fragment of the 105 kdalton subunit. Although there is considerable peptide overlap between the brush-border subunits and the 3 alpha-actinins, the peptide maps of the 95 and 105 kdalton proteins are substantially distinct from the various alpha-actinin maps, suggesting that neither brush-border subunit is a bona fide alpha-actinin. On the basis of peptide mapping criteria alone, one cannot exclude the possibility that the brush-border subunits are alpha-actinin-like. There is no immunological cross-reactivity between the brush-border subunits and alpha-actinins, using antibodies prepared against gizzard alpha-actinin.