Elements of the major myofibrillar binding peptide motif are present in the earliest of true muscle type creatine kinases

Origin of the genes for the isoforms of creatine kinase

Creatine kinase (CK) is a member of a family of phosphoryl transfer enzymes called phosphagen (guanidino) kinases which play a central role in cellular energy homeostasis. There are three CK isoform gene groups, each coding for proteins targeted to different intracellular compartments--cytoplasmic (CytCK), mitochondrial (MtCK) and flagellar (FlgCK). The former two CKs are either dimeric or octameric while FlgCKs are contiguous trimers consisting of three fused, complete CK domains. Conventional wisdom supports the view that CKs evolved from a cytoplasmic, monomeric ancestral protein closely related to a phosphagen kinase homologue, arginine kinase (AK). Recently, it has been shown that a demosponge (Phylum Porifera) expresses a true MtCK and two dimeric, protoflagellar CKs (protoflgCK) with great similarity to FlgCKs. To further probe the early evolution of CK, we have obtained additional sequences for Mt- and protoflgCKs from two more demosponges and from three hexactinellid (glass) sponges as well as an MtCK sequence from a basal metazoan cnidarian. Phylogenetic analyses using Maximum Likelihood (ML) of these new CK sequences with other CKs and phosphagen kinases yielded a consensus tree containing an assemblage of MtCKs and a supercluster consisting of protoflg-, Flg- and CytCKs. The MtCKs appear basal in the tree topology consistent with prior results. Within the protoflg-, Flg- and CytCK supercluster, the protoflgCKs appear to be allied to the domains of the FlgCKs, although the support is not robust. PCR amplification of genomic DNA and sequencing of the genes for Mt- and protoflgCK from the demosponge Suberites fuscus showed that the sponge MtCK shares four-five common intron:exon boundaries with invertebrate, protochordate and vertebrate MtCKs supporting a common ancestry and the extreme conservation of intron:exon organization in MtCK genes. The protoflgCK gene organization was highly divergent in relation to other CK genes but shares a common intron:exon boundary with domain 2 of the gene for the FlgCK from the tunicate Ciona intestinalis, providing support for the linkage of the protoflgCKs with the FlgCKs. Our results show that the two, major CK gene lineages are present in arguably the oldest, extant metazoan group, the hexactinellid sponges, indicating that these two genes are ancient and confirming prior work that the MtCK gene is likely basal and ancestral.

Comparison of kinetic constants of creatine kinase isoforms

The purpose of this study was to elucidate the functional differences between the CK isoforms by cloning the cDNAs of 12 CK isoforms: the M and B cytoplasmic forms and uMiCK from mouse, the M1, M2 and B cytoplasmic forms from Danio rerio, M1 and M2 cytoplasmic forms from the lower vertebrate Lampetra japonica, a cytoplasmic CK and a MiCK from the marine worm Neanthes diversicolor, and a cytoplasmic CK and a MiCK from the soft coral Dendronephthya gigantea. These were expressed in Escherichia coli as a fusion protein with maltose-binding protein, and kinetic constants (K(m), K(d) and k(cat)) of all the recombinant enzymes, except for the unstable Dendronephthya cytoplasmic CK, were determined for the forward reaction. The kinetic constants of the M- and B-forms of the mouse and Danio cytoplasmic CKs differed significantly, with the K(m) for creatine (K(m)Cr) of M-CK being three- to nine-fold higher than that of B-CK, possibly reflecting differences in the concentration of creatine in muscle and brain cells. The mouse uMiCK had the lowest K(m)Cr value among the CK isoforms. In addition, it also exhibited a strong synergism for substrate binding (K(d)/K(m)=11.8). These results indicate that uMiCK has unique characteristics compared with other CK isoforms. Two subisoforms of M-CK were found in the lower vertebrate L. japonica, and the kinetic constants of recombinant M1- and M2-CKs differed significantly. The M1- and M2-CKs were expressed in skeletal muscle with a ratio of 7:3, while M1-CK was the predominant subisoform in the testis. The kinetic constants of cytoplasmic CK from the marine worm Neanthes were significantly different from those of Neanthes MiCK, possibly indicating that functional differences among CK isoforms occurred at least before the divergence of annelids from other protostome invertebrates.

Evolution of the heart from bacteria to man

This review provides an overview of the evolutionary path to the mammalian heart from the beginnings of life (about four billion years ago ) to the present. Essential tools for cellular homeostasis and for extracting and burning energy are still in use and essentially unchanged since the appearance of the eukaryotes. The primitive coelom, characteristic of early multicellular organisms ( approximately 800 million years ago), is lined by endoderm and is a passive receptacle for gas exchange, feeding, and sexual reproduction. The cells around this structure express genes homologous to NKX2.5/tinman, and gradual specialization of this "gastroderm" results in the appearance of mesoderm in the phylum Bilateria, which will produce the first primitive cardiac myocytes. Investment of the coelom by these mesodermal cells forms a "gastrovascular" structure. Further evolution of this structure in the bilaterian branches Ecdysoa (Drosophila) and Deuterostoma (amphioxus) culminate in a peristaltic tubular heart, without valves, without blood vessels or blood, but featuring a single layer of contracting mesoderm. The appearance of Chordata and subsequently the vertebrates is accompanied by a rapid structural diversification of this primitive linear heart: looping, unidirectional circulation, an enclosed vasculature, and the conduction system. A later innovation is the parallel circulation to the lungs, followed by the appearance of septa and the four-chambered heart in reptiles, birds, and mammals. With differentiation of the cardiac chambers, regional specialization of the proteins in the cardiac myocyte can be detected in the teleost fish and amphibians. In mammals, growth constraints are placed on the heart, presumably to accommodate the constraints of the body plan and the thoracic cavity, and adult cardiac myocytes lose the ability to re-enter the cell cycle on demand. Mammalian cardiac myocyte innervation betrays the ancient link between the heart, the gut, and reproduction: the vagus nerve controlling heart rate emanates from centers in the central nervous system regulating feeding and affective behavior.

Evolution and Divergence of the Genes for Cytoplasmic, Mitochondrial, and Flagellar Creatine Kinases

Creatine kinase (CK) plays a central role in energy homeostasis in cells that display high and variable rates of energy turnover. A number of CK genes exist, each being targeted to particular intracellular compartments. In the vertebrates, two genes code for proteins which form homo- and heterodimers targeted to the cytoplasm, while two additional genes code for primarily octameric proteins targeted to the mitochondrial intermembrane space. Yet another gene is present in certain groups which codes for three fused, complete CK domains and is typically targeted to the flagellar membrane of primitive-type spermatozoa. CK is widely distributed in protochordates and both protostome and deuterostome invertebrate groups. The evolutionary relationships of these CK genes have not been fully elucidated. The present communication reports new cDNA-derived deduced amino acid sequences for four cytoplasmic and three mitochondrial CKs and one flagellar CK from lophotrochozoan, protostome invertebrates as well as a new cytoplasmic CK sequence from a protochordate tunicate. These new sequences, coupled with available sequences in the databases and sequences extracted from genome sequencing projects, provide revealing insights into the evolution and divergence of CK genes. Phylogenetic analyses showed that single cytoplasmic, mitochondrial, and flagellar CK genes were present prior to the divergence of the protostomes and deuterostomes. The flagellar CK gene may have evolved within the cytoplasmic gene clade, although the evidence is somewhat equivocal. The two cytoplasmic genes in the vertebrates, and most likely the two mitochondrial genes, evolved after the divergence of the craniates from the protochordates. Comparison of the structure of the genes for selected cytoplasmic, mitochondrial, and flagellar CKs revealed two identical intron boundaries, further reinforcing the notion of a common evolutionary origin, but also showed patterns of changes in structure consistent with each gene type. These studies show that the cytoplasmic, mitochondrial, and flagellar CK genes are rather ancient and that there has been a systematic pattern of duplication and divergence consistent with changing nature of energy demands and physicochemical environment in the cells where they are expressed.

Cloning and expression of mitochondrial and protoflagellar creatine kinases from a marine sponge: implications for the origin of intracellular energy transport systems

Creatine kinase (CK) plays a central role in energy transactions in cells displaying high and variable rates of ATP turnover. Cytoplasmic and mitochondrial CK genes code for isoforms which are targeted to distinct intracellular compartments often in close physical proximity to sites of ATP hydrolysis or synthesis. In certain lower groups a third CK gene is present which codes for a flagellar CK isoform consisting of three complete, fused CK domains. Recent work has shown that cytoplasmic, mitochondrial, and flagellar CKs are present in protochordates and in deuterostome and protostome invertebrates. We report here that the marine sponge Tethya aurantia, a representative of the oldest of all multi-cellular animal groups, expresses three unique CK transcripts. One of these CK transcripts codes for protein that has a mitochondrial targeting sequence and in a phylogenetic analysis is positioned at the base of the cluster containing mitochondrial CK sequences from invertebrates, protochordates, and vertebrates; it is clearly a mitochondrial CK. When expressed in Escherichia coli the mitochondrial form from T. aurantia was found to be dimeric unlike all other mitochondrial CKs which are typically octameric. The other two T. aurantia transcripts code for proteins that appear to be more closely related to flagellar CKs. These protoflagellar CKs were found to be dimers when expressed in Escherichia coli. Sponges last shared a common ancestor with higher animals as long as one billion years ago. The antiquity of intracellular localization, as evidenced by the presence of a true mitochondrial CK and protoflagellar CKs in the sponge T. aurantia, indicates that physical constraints on cellular energy transport were key, early driving forces in the evolution of this key enzyme system.