Previously, sequence comparisons between a mesophilic enzyme and a more the
rmostable homologue were shown to be a feasible approach to successfully pr
edict thermostabilizing amino acid substitutions. The 'consensus approach'
described in the present paper shows that even a set of amino acid sequence
s of homologous, mesophilic enzymes contains sufficient information to allo
w rapid design of a thermostabilized, fully functional variant of this fami
ly of enzymes. A sequence alignment of homologous fungal phytases was used
to calculate a consensus phytase amino acid sequence. Upon construction of
the synthetic gene, recombinant expression and purification, the first phyt
ase obtained, termed consensus phytase-1, displayed an unfolding temperatur
e (T-m) of 78.0 degreesC which is 15-22 degreesC higher than the T-m values
of all parent phytases used in its design. Refinement of the approach, com
bined with site-directed mutagenesis experiments, yielded optimized consens
us phytases with T-m values of up to 90.4 degreesC. These increases in T-m
are due to the combination of multiple amino acid exchanges which are distr
ibuted over the entire sequence of the protein and mainly affect surface-ex
posed residues; each individual substitution has a rather small thermostabi
lizing effect only. Remarkably, in spite of the pronounced increase in ther
mostability, catalytic activity at 37 degreesC is not compromised. Thus, th
e design of consensus proteins is a potentially powerful and novel alternat
ive to directed evolution and to a series of rational approaches for thermo
stability engineering of enzymes and other proteins. (C) 2000 Elsevier Scie
nce B.V. All rights reserved.