Motifs of Immunoglobulin-Like Domains: Neurotrophic Factor Receptors trk and trkB are Members of the Immunoglobulin Family

Abstract

The amino acid sequences of the 217 different Immunoglobulin (Ig)-like domains from 78 known members of the Ig family were compared for the four highly conserved segments and the frequencies of occurrence of amino acids at each position of the four segments were obtained as an amino acid versus position matrix. Using the frequency matrix as a probe, further Ig-related sequences were screened in NBRF database. It was found that trk and trkB proto-oncogene products, now known as receptors for neurotrophic factors, have two tandem repeats of the Ig-like domain in the extracellular region. Thus both trk and trkB are new members of the Ig family and they share structural similarity with a group of growth factor receptors with Ig-like domains in the extracellular region and protein tyrosine kinase in the intracellular region.