Zipper protein, a newly described tropomyosin-like protein of the intestinal brush border.

Abstract

We have cloned and sequenced from a chick intestinal library the cDNA for a new tropomyosin-like protein with an extensive leucine zipper motif. The cDNA recognized a 2.5-kilobase transcript with highest levels in the intestine. The open reading frame encoded a protein with 239 residues (28 kDa), the deduced sequence of which forms 27 heptad repeats, 21 of which begin with leucine and the other 6 with conservative substitutions (methionine, valine, threonine). This sequence predicts a coiled coil dimer similar to that of tropomyosin with which it has 34% homology. We have named this newly described protein zipper protein. The protein was expressed in bacteria. Antibodies were made to peptides representing different regions of the deduced sequence and tested for their ability to recognize the recombinant zipper protein on immunoblots. Such antibodies were used to immunolocalize zipper protein to the intestinal brush border. A radioimmunoassay was then established using recombinant zipper protein as standard and tracer and one of the affinity-purified antisera as primary antibody. Extracts from intestine, kidney, and liver displaced tracer zipper protein in parallel with that of the standard curve, and zipper protein levels were readily measured in those tissues to be 2.5 +/- 0.4, 0.34 +/- 0.03, and 0.15 +/- 0.03 micrograms/mg of protein, respectively. Brain contained no detectable zipper protein. We conclude that zipper protein is a tropomyosin-like protein found predominantly in the intestinal brush border; its location and structural similarity to tropomyosin suggest a possible role in regulating the interaction of brush border myosin 1 with the actin core of the microvillus.