The crystal structure of affinity-matured human growth hormone at 2 A resolution.Ultsch, M.H., Somers, W., Kossiakoff, A.A., de Vos, A.M.
(1994) J.Mol.Biol. 236: 286-299
- PubMed: 8107110
- DOI: 10.1006/jmbi.1994.1135
- PubMed Abstract:
- Affinity Maturation of Human Growth Hormone by Monovalent Phage Display
Lowman, H.B.,Wells, J.A.
() TO BE PUBLISHED --: --
A variant of human growth hormone (hGH), in which 15 mutations were introduced with phage display mutagenesis to improve receptor binding affinity by 400-fold, yielded two related crystal forms diffracting to high resolution. The structure of this va ...
A variant of human growth hormone (hGH), in which 15 mutations were introduced with phage display mutagenesis to improve receptor binding affinity by 400-fold, yielded two related crystal forms diffracting to high resolution. The structure of this variant was determined in both crystal forms, one at 2.0 A resolution and one at 2.4 A resolution, using molecular replacement with wild-type hGH taken from the receptor complex structure as a search model. Crystallographic refinement of the 2 A structure gave an R-value R-value of 18.5% for data in the resolution range 8 to 2 A. The final model consists of residues 1 to 128 and 155 to 191, with three side-chains modeled in alternative conformations, together with 77 water molecules. Comparison of the structure with wild-type hGH shows that most of the secondary structural elements are unchanged. The exception is the first turn of the third helix in the four-helix bundle core, which is unraveled in the present variant. Analysis of the two related packing environments suggests that this change is caused by crystal packing forces. A large change in the orientation of a short segment of helix found in the connection between the first two core helices is interpreted as evidence for rigid-body variability of this helical segment. Analysis of the mutations in light of the structure of the wild-type hGH/receptor complex shows that six of the mutations are buried in the hormone, whereas the remaining nine involve residues that interact with the receptor in the complex.
Department of Protein Engineering Genetech, Inc, South San Francisco, CA 94080.