Cooperative interactions in neurophysin‐neuropeptide hormonecomplexes

Abstract

The structural interdependence between neurophysin (NP) self‐association and ligand binding surfaces has been studied by analytical affinity chromatography of several NP sequence variants and derivatives on Met‐Tyr‐Phe‐aminobutyl‐agarose and bovine NP‐II Sepharose. Elutions of radiolabeled NP's from both matrices show that hybrid dimers can form between major bovine NP's (I and II, or VLDV‐ and MSEL‐NP's, respectively), as well as between human and bovine NP's, with affinities close to that for homologous dimer formation. Such evidence supports the view that the region of NP involved in NP‐NP contact is composed primarily of conserved structural elements of the protein. NP antibodies which recognize surfaces close to or in the NP‐NP contact region have been detected by their effects on bovine NP‐II elution on NP‐II Sepharose. Elutions of [3‐nitro‐Tyr 49] BNP‐II from Met‐Tyr‐Phe‐aminobutyl‐agarose showed that nitration has little effect on the chromatographic properties of NP‐II. This evidence substantiates previous arguments (Angal, S. & Chaiken, I.M. (1982) Biochemistry 21, 1574–1580) that the chromatographic behavior of native NP's on the affinity matrices is an expression of the interdependence of NP self‐association and ligand binding surfaces and not due to bivalent peptide binding by NP monomer. The affinity chromatographic properties of NP derivatives, including bovine NP‐II photolabeled in the ligand binding site and tryptic fragments of bovine