Trypanosoma congolense: Surface glycoproteins of two early bloodstream variants

Trypanosome variant-specific glycoproteins: a polygene protein family with multiple folding patterns?

“…There is a region of partial amino acid homology between 105 and 45 residues from the COOH terminus. Upstream of this there are only modest degrees of homology between some VSGs (23). The conservation of structure at the COOH terminus may be related to the known VSG-VSG and VSG-plasma membrane interaction.…”

Molecular biology of trypanosome antigenic variation.

“…In addition, carbohydrate residues are attached in an unknown fashion to the C-terminal aspartic acid or serine of the mature VSG as described below. Interestingly, these carbohydrate moieties are not antigenic when the VSG is attached to the trypanosome membrane, although they comprise a cross-reacting antigenic determinant on purified soluble-form VSGs (6,16,79).…”

The Surface of the African Trypanosomes1,2

“…Purification procedures follow either the early procedures of Cross (1 1) or the lectin-column based procedures (23, 40). From published data it is clear that partially purified VSG preparations may contain non-VSG constituents which are common to many serovariants and may constitute one possible cause for apparent VSG cross-reactivity (5). More recently, work has begun on the characterization of other, non-VSG surface proteins and glycoproteins (24).…”

“…Partial proteolysis studies show that partial tryptic digestion produces rapid digestion of the C-terminal portion of the VSG molecule, reducing in one instance the MW from 53,000 and to 48,000 (5). It has not proved possible to isolate the 5000 MW fragment.…”

“…What is unusual for a family of proteins subserving a similar function is that, except for the C-terminal region, there is little or no homology among most of the VSGs whose primary amino acid structure has been determined (12,32). Yet when a detailed comparison is made of the N-terminal region of two T. congolense VSGs from a relapsing infection, it becomes clear that when these polypeptides are aligned to give the greatest degree of amino acid homology, this alignment position gives also the least number of two-base differences between the coding base triplets for each amino acid residue (5). Such a pattern could arise where a single original gene has undergone a high degree of point mutational change.…”