A gene (vsp417-3A-II) encoding a new member
of the variant-specific surface protein (VSP) family of Giardia
is
described. Vsp417-3A-II is detected exclusively in
isolates belonging to the genetic Assemblage A/Group II sublineage
of
G. intestinalis, and it is closely related to a previously characterized
VSP gene (tsp11, herein renamed vsp417-2A-I)
found
in Group I isolates of G. intestinalis. Analysis of DNA amplified
from the genomes of Group II isolates using consensus
primers also revealed products corresponding to the vsp417-2 locus
(vsp417-2A-II allele), indicating that vsp417-2A-II
and vsp417-3A-II represent separate loci in these organisms.
Southern hybridizations revealed a single genomic copy of
vsp417-3A-II in Group II isolates, but efforts to detect
this locus in Group I organisms were unsuccessful. Together with
the vsp417-1 (tsa417) locus that was first identified
in the genetic Group I isolate WB and which has been detected since
in all tested genetic Group I isolates (as vsp417-1A-I)
and in genetic Group II isolates (as vsp417-1A-II),
vsp417-3A-II represents a third member of a stable
subset of tsa417-like VSP genes in genetic Group II G. intestinalis.
The encoded
polypeptide, vsp417-3A-II (667 residues, predicted
Mr 69120) possesses a high cysteine content (12·1
mol%), 28 copies
of the metal-binding -CXXC- motif, and a highly conserved C-terminal hydrophobic
domain – similar to all other
characterized Giardia VSP. A revised nomenclature for Giardia
VSP genes is proposed, prompted by the need to describe
the homologues found in the various major genotypes of the species complex,
G. intestinalis.
Purification of a Variant-specific Surface Protein ofGiardia lambliaand Characterization of its Metal-binding Properties
