The Glossina morsitans tsetse fly saliva: general characteristics and identification of novel salivary proteins

The tsetse fly (Glossina spp.) is an obligate blood-sucking insect that transmits different human-pathogenic and livestock threatening trypanosome species in Africa. To obtain more insight in the tsetse salivary function, some general aspects of the tsetse fly saliva and its composition were studied. Direct pH and protein content measurements revealed a moderately alkaline (pH approximately 8.0) salivary environment with approximately 4.3 microg soluble proteins per gland and a constant representation of the major saliva proteins throughout the blood-feeding cycle. Although major salivary genes are constitutively expressed, upregulation of salivary protein synthesis within 48 h after the blood meal ensures complete protein replenishment from day 3 onwards. Screening of a non-normalised Glossina morsitans morsitans lambdagt11 salivary gland expression library with serum from a saliva-immunized rabbit identified three full-length cDNAs encoding for novel salivary proteins with yet unknown functions: a 8.3 kDa glycine/glutamate-rich protein (G. morsitans morsitans salivary gland protein Gmmsgp1), a 12.0 kDa proline-rich protein (Gmmsgp2), and a 97.4 kDa protein composed of a metallophosphoesterase/5'nucleotidase region with a glutamate/aspartate/asparagines-rich region (Gmmsgp3).