Abstract
BackgroundBoth calcium signals and protein phosphorylation responses are universal signals in eukaryotic cell signaling. Currently three pathways have been characterized in different eukaryotes converting the Ca2+ signals to the protein phosphorylation responses. All these pathways have based mostly on studies in plants and animals.ResultsBased on the exploration of genomes and transcriptomes from all the six eukaryotic supergroups, we report here in Metakinetoplastina protists a novel gene family. This family, with a proposed name SCAMK, comprises SnRK3 fused calmodulin-like III kinase genes and was likely evolved through the insertion of a calmodulin-like3 gene into an SnRK3 gene by unequal crossover of homologous chromosomes in meiosis cell. Its origin dated back to the time intersection at least 450 million-year-ago when Excavata parasites, Vertebrata hosts, and Insecta vectors evolved. We also analyzed SCAMK’s unique expression pattern and structure, and proposed it as one of the leading calcium signal conversion pathways in Excavata parasite. These characters made SCAMK gene as a potential drug target for treating human African trypanosomiasis.ConclusionsThis report identified a novel gene fusion and dated its precise fusion time in Metakinetoplastina protists. This potential fourth eukaryotic calcium signal conversion pathway complements our current knowledge that convergent evolution occurs in eukaryotic calcium signaling.
Highlights
Both calcium signals and protein phosphorylation responses are universal signals in eukaryotic cell signaling
Based on the fact that Calcium dependent protein kinase (CDPK) is fused by interacting proteins CaM and CaMK [18], an intriguing yet unknown question is whether there is a convergent gene fusion occurred between CBL-interacting protein kinase (CIPK) and calcineurin Blike (CBL) (Additional file 1: Figure S1), similar to the fusion origin of CDPK
Discovery of a monophyletic gene group with a new structural constitution We first set out to identify whether or not there is another kind of Ca2+-activated protein kinases by searching all eukaryotic clades based on two criteria, (i) kinome annotations from representatives of five eukaryotic supergroups, Homo sapiens [30], Entamoeba histolytica [31], Arabidopsis thaliana [32], Leishmania major [33], Plasmodium falciparum [34], and (ii) proteins CDPK, CRK, calcium/calmodulin-dependent protein kinase (CCaMK), CIPK with biochemical evidence as the Ca2+ signatures/signals (CS) decoders [22]
Summary
Both calcium signals and protein phosphorylation responses are universal signals in eukaryotic cell signaling. Three pathways have been characterized in different eukaryotes converting the Ca2+ signals to the protein phosphorylation responses. All these pathways have based mostly on studies in plants and animals. Relying on specific types of signal decoding proteins, these CSs are converted into intracellular downstream protein phosphorylation responses (PPRs) [7, 8]. The type I pathway (Additional file 1: Figure S1) relies on the calmodulin (CaM) for receiving the CSs and convert them to PPRs with interacting kinases such as calcium/calmodulin-dependent protein kinase (CCaMK) [11], calcium /calmodulin-binding protein kinase (CBK) [12], calcium/calmodulin-dependent protein kinase I, II, IV (CAMKI, II, IV) [13]. Based on the fact that CDPK is fused by interacting proteins CaM and CaMK [18], an intriguing yet unknown question is whether there is a convergent gene fusion occurred between CIPK and CBL (Additional file 1: Figure S1), similar to the fusion origin of CDPK
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