Helix-coil energetics for helix formers and breakers reflect context and temperature: mutants of helically robust, guest-sensitive homopeptide hosts.
The natural amino acids are primarily helix breakers at the low assignment temperatures characteristic of many studies, but recent genomic analyses of thermophilic proteins suggest that at high temperatures, some breakers may become strong helix formers. Moreover, the breaker/former inventory has not been previously characterized at the physiologically relevant temperature of 37 degrees C. The versatility of 13C==O NMR chemical shifts as helicity reporters allows construction of two mutant peptide series, tailored to expand the range of temperature assignments for helical propensities and derived from the core hosts tL-Ala9XxxAla9-tL and tL-AlaNva4XxxNva4Ala9-tL, Nva=norvaline. For three limiting guests Xxx, the helix former Nva and the breakers Gly and Pro, we report wXxx[T] assignments at seven temperatures from 2 to 80 degrees C, validating our reasoning and paving the way for assignment of a definitive wXxx[T] data-base.
Nasr
Khaled A
KA
Department of Chemistry, Room 6-433, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Schubert
Christian R
CR
Török
Marianna
M
Kennedy
Robert J
RJ
Kemp
Daniel S
DS
D000596:Amino Acids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013696:Temperature; D013816:Thermodynamics
D000596:Amino Acids; D050505:Mutant Proteins; D010455:Peptides