@entity369 kinase (AK) was isolated from the longitudinal muscle of the sea @entity9688 @entity20874 . Unlike the monomeric 40 kDa AKs from molluscs and arthropods, but like the cytoplasmic isoenzymes of vertebrate @entity908 kinase (CK), the Stichopus enzyme was dimeric. To explore the evolutionary origin of the dimeric AK, we determined its cDNA-derived @entity535 sequence of 370 residues. A comparison of the sequence with those of other enzymes belonging to the phosphagen kinase family indicated that the entire @entity535 sequence of Stichopus AK is apparently much more similar to vertebrate CKs than to all other AKs. A phylogenetic tree also strongly suggests that the Stichopus AK has evolved from CK. These results support the conclusion that AK evolved at least twice during the evolution of phosphagen kinases: first at an early stage of @entity69907 kinase evolution (its descendants are molluscan and arthropod AKs) and secondly from CK later in metazoan evolution. A comparison of the @entity535 sequence around the @entity6542 ( @entity6542 ) region (which is a possible candidate for the @entity2097 substrate recognition site in the phosphagen kinase family) of the Stichopus enzyme with those of other phosphagen kinases showed that the @entity6542 region of the Stichopus enzyme was of the AK type: five @entity535 deletions in the flexible loop region that might help to accommodate larger @entity2097 substrates in the active site. The presence of the AK-type deletions in the Stichopus AK, even though it seems that the enzyme's most immediate ancestor was probably CK, strongly suggests that the @entity6542 region has a role in substrate specificity. Stichopus AK and presumably other echinoderm AKs seem to have evolved from the CK gene; the sequence of @entity6542 region might have been replaced by the AK type via exon shuffling. The presence of an intron near the @entity6542 region in the Stichopus AK gene supports this hypothesis.

@entity369 kinase evolved twice: evidence that echinoderm @entity369 kinase originated from XXXX kinase.

@entity6542 :: ('MESH:C562465', 'Disease') :: ['guanidino specificity', 'GS'] @entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity908 :: ('MESH:D003401', 'Chemical') :: ['creatine'] @entity20874 :: ('307972', 'Species') :: ['Stichopus japonicus'] @entity9688 :: ('3659', 'Species') :: ['cucumber'] @entity2097 :: ('MESH:D019791', 'Chemical') :: ['guanidine'] @entity69907 :: ('CHEBI:64618', 'Chemical') :: ['phosphagen'] @entity369 :: ('CHEBI:29016', 'Chemical') :: ['Arginine']
@entity908 :: (MESH:D003401,Chemical) :: ['creatine']
