The Relaxin-Like Factor
Testicular Leydig cells contain the message for a protein of the insulin/relaxin-like family which, in the heat of discovery, was called the Leydig insulin-like peptide (LEY I-L)1 or INSL3, corresponding to the chromosomal location of the human gene.2 The authors felt that this was a Leydig cell specific message and predicted an insulin-like character for the gene product.1 Upon close scrutiny one will notice that the critical position in the A chain-loop, which decides between insulin or relaxin-like conformations, was occupied by glycine (relaxin configuration) instead of isoleucine (insulin configuration). Furthermore, the cDNA sequence of the B-chain also showed more relaxin-like characteristics, in particular the binding-site sequence RXXXR which occurred four residues further toward the C-terminal end of the molecule (Fig. 16.1). This meant a displacement of exactly one helix turn with the arginines still projecting essentially away from the core as they do in relaxin. All this was enough reason to synthesize the molecule according to the cDNA sequence and to study its physicochemical and biological properties. Within a month this new factor was synthesized and measurements of circular dichroism as a function of wavelength showed a conformation very similar to that of porcine relaxin.3 A tracer was produced by direct iodination of a synthetic precursor as given below.
KeywordsHigh Performance Liquid Chromatography Glycine Cysteine Arginine Alanine
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