Fig. 1. S. domuncula arginine kinase. (A) The sponge deduced protein (AK_SUBDO) is aligned with the arginine kinase from the Cnidarian Anthopleura japonica (KARG_ANTJA, O15992; Suzuki et al., 1997), and Drosophila melanogaster (AK_DROME, AAA68172, glycocyamine kinase from Nereis virens (GLYCAM_NEREIS, AAL26699 and human creatine kinase (CK_HUMAN, AAC31758 Mariman et al., 1987). Residues conserved (similar or related with respect to their physico-chemical properties) in all sequences are shown in white on black and those in at least three sequences in black on gray. The two characteristic domains for the ATP:guanido phosphotransferases, the N-terminal domain (ATP_GUA_N) and the C-terminal catalytic domain (ATP_GUA_C), are marked. The A. japonica arginine kinase is a two-domain enzyme, so the two phosphotransferase domains are also marked for this protein. The residues involved in coordinating Mg²⁺ to ATP are marked [ATP]. (B) Radial, unrooted phylogenetic tree, which includes the above mentioned sequences; the two domain enzyme from A. japonica has been split into the N-terminal and C-terminal segments (KARGn_ANTJA, aa₁ to aa₃₆₇; KARGc_ANTJA, aa₃₆₈ to aa₇₁₅). Shown in addition are the deuterostomian related sequence from (1) the Holothuria Stichopus japonicus (AK_STICJA, BAA76385, (2) the insect Schistocerca americana (AK_SCHIAM, AAC478301), (3) the mollusks Solen strictus (Bivalvia) (AK_SOLSTRI, BAB91358 N terminus aa₁ to aa₃₇₂ and C terminus aa₃₇₃ to aa₇₂₄; Suzuki et al., 2002), Corbicula japonica (Bivalvia) (AK_CORBJA, BAB913571; N terminus aa₁ to aa₃₇₂ and C terminus aa₃₇₃ to aa₇₂₃; Suzuki et al., 2002) and Ensis directus (Bivalvia) (AK_ENSIS, AAM906981; N terminus aa₁ to aa₃₇₂ and C terminus aa₃₇₃ to aa₇₂₃; Compaan and Ellington, 2003), (4) the oyster Crassostrea gigas (Bivalvia) (AK_CRASGI, BAD119501), (5) Crustaceans Homarus gammarus (KARG_HOMGA, 538542), Eriocheir sinensis (AK_ERISI, AAF43437 and Artemia franciscana (KARG_ARTSF, Q95V58), and (6) the nematode Caenorhabditis elegans (AK_CAEEL, NP_492714.1). Gene duplications within the mollusks and the Cnidarian taxa are indicated (D). The scale bar indicates an evolutionary distance of 0.1aa substitutions per position in the sequence.