Skip to main content

Table 2 Roles deduced for some of the residues which are conserved in the eukaryotic SiaT superfamily and whose mutations have been experimentally characterized#

From: Fold-recognition and comparative modeling of human α2,3-sialyltransferases reveal their sequence and structural similarities to CstII from Campylobacter jejuni

Mutant Equivalent residue in ST3Gal I Km(μM) Donor/Acceptor Activity Role deduced for the mutated residue from the modeled 3-D structures
Mutations in L motif
Wild type   50/331 100%  
C181A C142 -/- < 5% Structural role: involved in disulphide bridge
V184A V145 300/372 ~45% Structural role: part of hydrophobic core
L190A L151 597/188 ~28% Structural role: part of hydrophobic core
R207A R168 -/- < 5% Structural role: is buried and hydrogen bonds with side chains of N147 and E178 (ST3Gal I numbering). N147 is replaced by Ser in ST3Gal V, but Ser does not form hydrogen bond with Arg
V220A V181 343/260 30% Structural role: part of the hydrophobic core
S222A T183 -/- < 5% Structural role: These are at beginning of strand β4 and are solvent exposed
K223A K184 330/400 32%  
T225A T186 160/200 27%  
Mutations in S motif§
Wild type   50/330 100  
P318A P267 -/- very low Structural role: helix J nucleator
S319A S268 -/- < 5% Functional role: close to ribose
C332A C281 -/- < 5% Structural role: forms disulphide bridge
V335L V284 80/322 79% Structural role: part of the hydrophobic core
V335A V284 89/947 83%  
Mutations in motif-III*
H299A   -/- loss of activity Functional role: close to phosphate
Y300A   -/-   
  1. #Residues that are either strictly conserved or have conservative replacements in the eukaryotic SiaT superfamily are from [11].
  2. Data corresponds to mutants of ST6Gal I [8]. Hyphen (" - ") indicates values could not be determined.
  3. §Data corresponds to mutants of ST6Gal I [9]. Hyphen (" - ") indicates values could not be determined.
  4. *Data corresponds to mutants of ST3Gal I [7]. Hyphen (" - ") indicates values could not be determined.
  5. The mutation is considered structural if it destabilizes the structure and is far from functional site and it is termed functional if it is part of the substrate binding site.
  6. Are part of the same hydrophobic core.