Chemical modification of a variant of human MIP-1 alpha; implications for dimer structure

A sequence valiant of human MIP-1 alpha, in which Asp26 has been replaced b y Ala, has been chemically modified by the addition of C-13-labeled methyl groups at each of the lysine residues and the N-terminus. The sites of meth ylation have been verified by a combination of MALDI-TOF mass spectrometric experiments and tryptic digestion followed by N-terminal mapping. The effe ct of the modification on the structure and activity of the protein have be en determined by analytical ultra-centrifugation, C-13 NMR spectroscopy and receptor binding studies. The results of these experiments suggest that hu MIP-1 alpha D26A (BB10010), when present as a dimer, adopts a globular stru cture, like MCP-3, rather than the elongated or cylindrical structure deter mined for dimers of huMIP-1 beta and RANTES.