1DI4

ROLE OF AMINO ACID RESIDUES AT TURNS IN THE CONFORMATIONAL STABILITY AND FOLDING OF HUMAN LYSOZYME

Summary for 1DI4

• Entry DOI: 10.2210/pdb1di4/pdb
• Related: 1CJ6 1DI3 1DI5
• Descriptor: LYSOZYME C, SODIUM ION (3 entities in total)
• Functional Keywords: stability, turn, mutant, hydrolase
• Biological source: Homo sapiens (human)
• Cellular location: Secreted: P61626
• Total number of polymer chains: 1
• Total formula weight: 14615.55

Authors

Takano, K.,Yamagata, Y.,Yutani, K. (deposition date: 1999-11-29, release date: 1999-12-08, Last modification date: 2011-07-13)

Primary citation

Takano, K.,Yamagata, Y.,Yutani, K.
Role of amino acid residues at turns in the conformational stability and folding of human lysozyme.
Biochemistry, 39:8655-8665, 2000

PubMed Abstract: To clarify the role of amino acid residues at turns in the conformational stability and folding of a globular protein, six mutant human lysozymes deleted or substituted at turn structures were investigated by calorimetry, GuHCl denaturation experiments, and X-ray crystal analysis. The thermodynamic properties of the mutant and wild-type human lysozymes were compared and discussed on the basis of their three-dimensional structures. For the deletion mutants, Delta47-48 and Delta101, the deleted residues are in turns on the surface and are absent in human alpha-lactalbumin, which is homologous to human lysozyme in amino acid sequence and tertiary structure. The stability of both mutants would be expected to increase due to a decrease in conformational entropy in the denatured state; however, both proteins were destabilized. The destabilizations were mainly caused by the disappearance of intramolecular hydrogen bonds. Each part deleted was recovered by the turn region like the alpha-lactalbumin structure, but there were differences in the main-chain conformation of the turn between each deletion mutant and alpha-lactalbumin even if the loop length was the same. For the point mutants, R50G, Q58G, H78G, and G37Q, the main-chain conformations of these substitution residues located in turns adopt a left-handed helical region in the wild-type structure. It is thought that the left-handed non-Gly residue has unfavorable conformational energy compared to the left-handed Gly residue. Q58G was stabilized, but the others had little effect on the stability. The structural analysis revealed that the turns could rearrange the main-chain conformation to accommodate the left-handed non-Gly residues. The present results indicate that turn structures are able to change their main-chain conformations, depending upon the side-chain features of amino acid residues on the turns. Furthermore, stopped-flow GuHCl denaturation experiments on the six mutants were performed. The effects of mutations on unfolding-refolding kinetics were significantly different among the mutant proteins. The deletion/substitutions in turns located in the alpha-domain of human lysozyme affected the refolding rate, indicating the contribution of turn structures to the folding of a globular protein.

PubMed: 10913274
DOI: 10.1021/bi9928694

Experimental method

X-RAY DIFFRACTION (2 Å)