@entity68619 kinase (HTK) is a member of the highly conserved family of phosphagen kinases that includes @entity908 kinase (CK) and @entity369 kinase (AK). HTK is found only in sipunculid worms, and it shows activities for both the substrates @entity68619 and @entity47495 . Determining how HTK evolved in sipunculids is particularly insightful because all sipunculid-allied animals have AK and only some sipunculids have HTK. We determined the cDNA sequence of HTK from the sipunculid worm Siphonosoma cumanense for the first time, cloned it in pMAL plasmid and expressed it in @entity526 as a fusion protein with maltose-binding protein. The cDNAderived @entity535 sequence of Siphonosoma HTK showed high @entity535 identity with molluscan AKs. Nevertheless, the recombinant enzyme of Siphonosoma HTK showed no activity for the substrate @entity369 , but showed activity for @entity47495 . Comparison of the @entity535 sequences of HTK and AK indicated that the @entity535 residues necessary for the binding of the substrate @entity369 in AK have been completely lost in Siphonosoma HTK sequence. The phylogenetic analysis indicated that the HTK @entity535 sequence was placed just outside the molluscan AK cluster, which formed a sister group with the arthropod and @entity2199 AKs. These results suggest that Siphonosoma HTK evolved from a gene for molluscan AK. Moreover, to confirm this assertion, we determined by PCR that the gene for Siphonosoma HTK has a 5-exon/4-intron structure, which is homologous with that of the molluscan AK genes. Further, the positions of splice junctions were conserved exactly between the two genes. Thus, we conclude that Siphonosoma HTK has evolved from a primordial gene for molluscan AK.

@entity68619 kinase evolved from a gene for XXXX kinase.

@entity2199 :: ('6239', 'Species') :: ['nematode'] @entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity908 :: ('MESH:D003401', 'Chemical') :: ['creatine'] @entity47495 :: ('MESH:C009558', 'Chemical') :: ['taurocyamine'] @entity68619 :: ('CHEBI:16209', 'Chemical') :: ['hypotaurocyamine', 'Hypotaurocyamine'] @entity369 :: ('CHEBI:29016', 'Chemical') :: ['arginine'] @entity526 :: ('562', 'Species') :: ['E. coli']
@entity369 :: (CHEBI:29016,Chemical) :: ['arginine']
