Structural similarities between Thy-1 antigen from rat brain and immunoglobulin

Abstract

The molecular basis of cellular interactions is poorly understood but it is commonly believed that direct interactions between membrane-borne ligands and receptors are important. Membrane molecules whose expression is regulated in differentiation are candidates for these roles. Functional assays for cellular interactions are of such complexity that the traditional biochemical methods of purifying a molecule by following a functional assay are not applicable. It can be argued that the best approach is first to identify cell-surface molecules and then to attempt to identify functions on the basis of their molecular characteristics or by using the molecules or antibodies to them to perturb functional systems¹. The Thy-1 (theta) antigen has been much studied because it is expressed in large amounts on some cell types but is absent from others. Thy-1 is probably the most abundant cell surface glycoprotein of rodent brain and thymus, yet its function is unknown (reviewed in ref. 2). On the basis of structural studies it was suggested that Thy-1 would be a candidate for displaying ligands for cell interactions and that the specific determinants involved might be carbohydrate³. We present here a preliminary report of further structural work dealing with the amino acid sequence and circular dichroism (CD) spectrum of rat brain Thy-1. The results suggest that this molecule has a structure resembling an Ig domain, which would not be consistent with an enzymatic function. The molecule probably exists to be recognised and the determinants involved could be protein or carbohydrate.