A beta-helical antifreeze protein isoform with increased activity. Structural and functional insights.
The insect spruce budworm (Choristoneura fumiferana)(Cf) produces a number of isoforms of its highly active antifreeze protein (CfAFP). Although most of the CfAFP isoforms are in the 9-kDa range, isoforms containing a 30- or 31-amino acid insertion have also been identified. Here we describe the functional and structural analysis of a selected long isoform, CfAFP-501. X-ray crystal structure determination reveals that the 31-amino acid insertion found in CfAFP-501 forms two additional loops within its highly regular beta-helical structure. This effectively extends the area of the two-dimensional Thr array and ice-binding surface of the protein. The larger isoform has 3 times the thermal hysteresis activity of the 9-kDa CfAFP-337. As well, a deletion of the 31-amino acid insertion within CfAFP-501 to form CfAFP-501-Delta-2-loop, results in a protein with reduced activity similar to the shorter CfAFP isoforms. Thus, the enhanced antifreeze activity of CfAFP-501 is directly correlated to the length of its beta-helical structure and hence the size of its ice-binding face.
Leinala
Eeva K
EK
Departments of Biochemistry and Biology, Queen's University, Kingston, Ontario, K7L 3N6 Canada.
Davies
Peter L
PL
Doucet
Daniel
D
Tyshenko
Michael G
MG
Walker
Virginia K
VK
Jia
Zongchao
Z
D000818:Animals; D021301:Antifreeze Proteins / Q000737:chemistry* / Q000502:physiology*; D018360:Crystallography, X-Ray; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism; D019476:Insect Proteins / Q000737:chemistry* / Q000502:physiology*; D007313:Insecta; D008958:Models, Molecular; D011485:Protein Binding; D017510:Protein Folding; D020033:Protein Isoforms; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013912:Threonine / Q000737:chemistry
D021301:Antifreeze Proteins; D018076:DNA, Complementary; D019476:Insect Proteins; D020033:Protein Isoforms; D013912:Threonine