Crystal structures of trypanosomal histidyl-tRNA synthetase illuminate differences between eukaryotic and prokaryotic homologs.
Crystal structures of histidyl-tRNA synthetase (HisRS) from the eukaryotic parasites Trypanosoma brucei and Trypanosoma cruzi provide a first structural view of a eukaryotic form of this enzyme and reveal differences from bacterial homologs. HisRSs in general contain an extra domain inserted between conserved motifs 2 and 3 of the Class II aminoacyl-tRNA synthetase catalytic core. The current structures show that the three-dimensional topology of this domain is very different in bacterial and archaeal/eukaryotic forms of the enzyme. Comparison of apo and histidine-bound trypanosomal structures indicates substantial active-site rearrangement upon histidine binding but relatively little subsequent rearrangement after reaction of histidine with ATP to form the enzyme's first reaction product, histidyladenylate. The specific residues involved in forming the binding pocket for the adenine moiety differ substantially both from the previously characterized binding site in bacterial structures and from the homologous residues in human HisRSs. The essentiality of the single HisRS gene in T. brucei is shown by a severe depression of parasite growth rate that results from even partial suppression of expression by RNA interference.
Department of Biochemistry, University of Washington, Seattle, WA 98195, USA. merritt@u.washington.edu <merritt@u.washington.edu>
Ethan A
EA
Merritt
Tracy L
TL
Arakaki
J Robert
JR
Gillespie
Eric T
ET
Larson
Angela
A
Kelley
Natascha
N
Mueller
Alberto J
AJ
Napuli
Jessica
J
Kim
Li
L
Zhang
Christophe L M J
CL
Verlinde
Erkang
E
Fan
Frank
F
Zucker
Frederick S
FS
Buckner
Wesley C
WC
van Voorhis
Wim G J
WG
Hol
D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D055785:Gene Knockdown Techniques; D020043:Genes, Essential; D006643:Histidine-tRNA Ligase / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D016415:Sequence Alignment; D014346:Trypanosoma brucei brucei / Q000737:chemistry / Q000201:enzymology*; D014349:Trypanosoma cruzi / Q000737:chemistry / Q000201:enzymology*
D006643:Histidine-tRNA Ligase