This family is found in Trypanosome species, and appears to be one of two invariant surface glycoproteins, ISG65 and ISG75. that are found in the mammalian stage of the parasitic protozoan. the sequence suggests the two families are polypeptides with N-terminal signal sequences, hydrophilic extracellular domains, single trans-membrane alpha-helices and short cytoplasmic domains. they are both expressed in the bloodstream form but not in the midgut stage. Both polypeptides are distributed over the entire surface of the parasite [1,2].

1: Molecular characterization of two invariant surface glycoproteins specific for the bloodstream stage of Trypanosoma brucei. Ziegelbauer K, Multhaup G, Overath P; J Biol Chem. 1992;267:10797-10803. PMID:1587856

2: Heterologous expression, purification and characterisation of the extracellular domain of trypanosome invariant surface glycoprotein ISG75. Tran T, Buscher P, Vandenbussche G, Wyns L, Messens J, De Greve H; J Biotechnol. 2008;135:247-254. PMID:18538880