Engineering hyperthermostability into a GH11 xylanase is mediated by subtle changes to protein structure.
Understanding the structural basis for protein thermostability is of considerable biological and biotechnological importance as exemplified by the industrial use of xylanases at elevated temperatures in the paper pulp and animal feed sectors. Here we have used directed protein evolution to generate hyperthermostable variants of a thermophilic GH11 xylanase, EvXyn11. The Gene Site Saturation Mutagenesis (GSSM) methodology employed assesses the influence on thermostability of all possible amino acid substitutions at each position in the primary structure of the target protein. The 15 most thermostable mutants, which generally clustered in the N-terminal region of the enzyme, had melting temperatures (Tm) 1-8 degrees C higher than the parent protein. Screening of a combinatorial library of the single mutants identified a hyperthermostable variant, EvXyn11TS, containing seven mutations. EvXyn11TS had a Tm approximately 25 degrees C higher than the parent enzyme while displaying catalytic properties that were similar to EvXyn11. The crystal structures of EvXyn11 and EvXyn11TS revealed an absence of substantial changes to identifiable intramolecular interactions. The only explicable mutations are T13F, which increases hydrophobic interactions, and S9P that apparently locks the conformation of a surface loop. This report shows that the molecular basis for the increased thermostability is extraordinarily subtle and points to the requirement for new tools to interrogate protein folding at non-ambient temperatures.
Dumon
Claire
C
Institute for Cell and Molecular Biosciences, Newcastle University, The Medical School, Newcastle Upon Tyne NE2 4HH, United Kingdom.
Varvak
Alexander
A
Wall
Mark A
MA
Flint
James E
JE
Lewis
Richard J
RJ
Lakey
Jeremy H
JH
Morland
Carl
C
Luginbühl
Peter
P
Healey
Shaun
S
Todaro
Thomas
T
DeSantis
Grace
G
Sun
May
M
Parra-Gessert
Lilian
L
Tan
Xuqiu
X
Weiner
David P
DP
Gilbert
Harry J
HJ
D003062:Codon; D017931:DNA Primers; D004355:Drug Stability; D043364:Endo-1,4-beta Xylanases / Q000737:chemistry* / Q000235:genetics; D015723:Gene Library; D016133:Polymerase Chain Reaction; D015202:Protein Engineering / Q000379:methods*; D013816:Thermodynamics
D003062:Codon; D017931:DNA Primers; D043364:Endo-1,4-beta Xylanases