C
at
al
ase-peroxid
ases (K
atGs)
are heme peroxid
ases with homology to ye
ast cytochrome
cperoxid
ase (CCP)
and pl
ant
ascorb
ate peroxid
ases (APXs). K
atGs exhibit
a peroxid
ase
activity of bro
adspecificity
and
a high c
at
al
ase
activity, which strongly depends on the presence of
a dist
al Trp
as p
art ofthe conserved
amino
acid tri
ad Arg-Trp-His. By contr
ast, both CCP
and APX do not h
ave
a subst
anti
alc
at
al
ase
activity despite the presence of the s
ame tri
ad. Thus, to elucid
ate structure-function rel
ationshipsof c
at
al
ase-peroxid
ases (for which no cryst
al structure is
av
ail
able
at the moment), we performed UV-Vis
and reson
ance R
am
an studies of recombin
ant wild-type K
atG from the cy
anob
acterium
SynechocystisPCC 6803
and the dist
al side v
ari
ants (His123
![](/im<font color=)
ages/entities/r
arr.gif">Gln, Glu; Arg119
![](/im<font color=)
ages/entities/r
arr.gif">Al
a, Asn; Trp122
![](/im<font color=)
ages/entities/r
arr.gif">Phe, Al
a). Thedist
al c
avity of K
atG is very simil
ar to th
at of the other cl
ass I peroxid
ases. A H-bond network involvingw
ater molecules
and the dist
al Trp, Arg,
and His is present, which connects the dist
al
and proxim
al sidesof the heme pocket. However, dist
al mut
ation not only
affects the heme Fe coordin
ation st
ate
and perturbsthe proxim
al Fe-Im bond,
as previously observed for other peroxid
ases, but
also
alters the st
ability ofthe heme
architecture. The ch
arge of the dist
al residues
appe
ars p
articul
arly import
ant for m
aint
aining theheme
architecture. Moreover, the Trp pl
ays
a signific
ant role in the dist
al H-bonding, much morepronounced th
an in CCP. The relev
ance of these findings for the c
at
al
ase
activity of K
atG is discussed inlight of the complete loss of c
at
al
ase
activity in the dist
al Trp mut
ants.