A New Family of Receptor Tyrosine Kinases with a Venus Flytrap Binding Domain in Insects and Other Invertebrates Activated by Aminoacids

Abstract

BackgroundTyrosine kinase receptors (RTKs) comprise a large family of membrane receptors that regulate various cellular processes in cell biology of diverse organisms. We previously described an atypical RTK in the platyhelminth parasite Schistosoma mansoni, composed of an extracellular Venus flytrap module (VFT) linked through a single transmembrane domain to an intracellular tyrosine kinase domain similar to that of the insulin receptor.Methods and FindingsHere we show that this receptor is a member of a new family of RTKs found in invertebrates, and particularly in insects. Sixteen new members of this family, named Venus Kinase Receptor (VKR), were identified in many insects. Structural and phylogenetic studies performed on VFT and TK domains showed that VKR sequences formed monophyletic groups, the VFT group being close to that of GABAB receptors and the TK one being close to that of insulin receptors. We show that a recombinant VKR is able to autophosphorylate on tyrosine residues, and report that it can be activated by L-arginine. This is in agreement with the high degree of conservation of the alpha amino acid binding residues found in many amino acid binding VFTs. The presence of high levels of vkr transcripts in larval forms and in female gonads indicates a putative function of VKR in reproduction and/or development.ConclusionThe identification of RTKs specific for parasites and insect vectors raises new perspectives for the control of human parasitic and infectious diseases.

Characterization of the Src/Abl Hybrid Kinase SmTK6 of Schistosoma mansoni

“…cRNA was also produced from a pcDNA 3.1 plasmid encoding full-length SmVKR1 (23) rendered constitutively active by an exchange of the Phe-1167 (close to the potential YY1064 -1065 autophosphorylation site) to a glutamic acid residue (SmVKR1 YYRE ) performed by site-directed mutagenesis as described before (24,25). SmVKR1 YYRE -C-term was amplified by PCR from SmVKR1 YYRE in pcDNA 3.1 using the primer pair SmVKR1-C-term-5Ј (5Ј-CCCTGCAGTCAAGGTAGAA-ACGCTAAACTGTTATC-3Ј; containing a PstI site) and SmVKR1-C-term-3Ј (5Ј-GGGAATTCCGACGTAAACTGA-AAGAAATTGAAAATCG-3Ј; containing an EcoRI site) and subcloned in the T7-containing plasmid PGBKT7 that also contains the Myc tag.…”

“…SmVKR1 (previously called SmRTK-1) was described as an unusual schistosome RTK composed of an extracellular Venus Flytrap module (a ligand-binding domain in class 3 G-proteincoupled receptors) linked by a single transmembrane domain to a TK domain, which displayed similarity to that of insulin receptors (23). Venus kinase receptors have been found in different invertebrates, particularly in insects (24). As in schistosomes, Venus kinase receptors are mainly expressed in female gonads, indicating a putative function of these receptors in reproduction and/or development.…”

Ovary ecdysteroidogenic hormone requires a receptor tyrosine kinase to activate egg formation in the mosquito Aedes aegypti

“…1B). It also contained 10 predicted N-glycosylation sites plus a Venus flytrap (VFT) module known from several proteins including a subset of RTKs in insects and other invertebrates (23,24). Quantitative real-time PCR (qRT-PCR) indicated that AAEL001915 expression was higher in the ovaries of 5-d-old nonblood female A. aegypti than in the fat body and midgut (Fig.…”

“…VFT modules are known from several types of membrane proteins including bacterial periplastic proteins and select GPCRs and RGCs (23). In contrast, VFT modules are unknown in PRKs, with the exception of a subset of RTKs in arthropods and select other invertebrate phyla recently named the Venus Kinase Receptor family (23,30). All genes in the OR1 clade of our dipteran phylogeny are members of this assemblage.…”

“…The native ligand(s) for these receptors is unknown, although expression in Xenopus oocytes indicates L-arginine and calcium activate SmVKR1 and downstream signaling of the PI3K/Akt/S6K pathway (33). An in vitro assay also showed that L-arginine stimulated phosphorylation of a VFT-containing RTK from the honey bee, Apis mellifera, expressed in a human cell line (23). In contrast, our results argue against amino acids or calcium activating AAEL001915, given the media (Sf-900 or SFX) used in our in vitro experiments contain an abundance of both, yet ovaries produce no ECD and S2 cells show no evidence of Akt phosphorylation in the absence of OEH or ILP3 (Figs.…”