REFINED CRYSTAL-STRUCTURE AND MUTAGENESIS OF HUMAN GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR

The crystal structure of recombinant human wgranulocyte-macrophage col ony stimulating factor(rhGM-CSF) has been refined against data extendi ng to a resolution of similar to 2.4 Angstrom along a and similar to 1.9 Angstrom along b and c*. Anisotropic scale factors of B-11 = -20. 8 Angstrom(2), B-22 = 7.4 Angstrom(2), B-33 = 13.3 Angstrom(2) correct ed for the more rapid fall of diffraction in the a direction. The ani sotropy correlates with the weak crystal packing interactions along th e a axis, In addition to apolar side chains in the protein core, there are 10 buried hydrogen bonding residues, Those residues involved in i ntramolecular hydrogen bonding to main chain atoms are better conserve d than those hydrogen bonding to other side chain atoms; 24 solvation sites are observed at equivalent positions in the two molecules in the asymmetric unit, and the strongest among these are located in clefts between secondary structural elements, No buried water sites are seen, Two surface clusters of hydrophobic side chains are located near the expected receptor binding regions, Mutagenesis of 11 residues on the h elix A/helix C face confirms the importance of Glu-21 and shows that G ly-75 and Gln-86, located on helix C, each causes-greater than fourfol d drop in activity, Glu-21 and Gly-75, but not Gln-86, are structurall y equivalent to residues involved in the growth hormone binding to its receptor. (C) 1996 Wiley-Liss, Inc.