Complete primary structure of a scallop striated muscle myosin heavy chain. Sequence comparison with other heavy chains reveals regions that might be critical for regulation

Population transcriptomics reveals the effect of gene flow on the evolution of range limits

One of the most important questions in evolutionary biology is how the spatial distribution of species is limited. Asymmetric gene flow from core populations is suggested to increase the number of poorly adapted immigrants in the populations at the range edge. Genetic load due to migration, i.e., migration load, should prevent adaptation to the local habitat, leading to decreases in distribution range via local extinction or the limiting range expansion. However, few experimental studies have examined the effects of immigration on fitness and natural selection within recipient populations. To investigate the influence of migration load on the evolution of distribution range, we performed field and laboratory observations as well as population transcriptomics for the common river snail, Semisulcospira reiniana. This species meets the conditions that migration from source populations can prevent local adaptation in a sink population because they inhabit the broader range of environments, including middle/upper reaches of a river and estuaries within a single river and they may be more vulnerable to being swept away by water currents due to lowered spontaneous (upward) locomotion activity. We found that river steepness was related to the lower distribution limit of S. reiniana, with a narrower distribution range in the steeper river. Population transcriptomic analysis showed that gene flow was heavily asymmetric from the upstream populations to downstream ones in the steep river, suggesting a greater migration load in the steep river. The number of genes putatively involved in adaptation to the local habitat was lower in the steep river than in the gentle river. Gene expression profiles suggested that individuals achieve better local adaptation in the gentle river. Laboratory experiments suggested that evolutionary differences in salinity tolerance among local populations were only found in the gentle river. Our results consistent with the hypothesis that migration load owing to asymmetric gene flow disturbs local adaptation and restricts the distribution range of river snails.

Striated myosin heavy chain gene is a crucial regulator of larval myogenesis in the pacific oyster Crassostrea gigas

Pacific oyster (Crassostrea gigas), the most productive economical bivalve mollusc, is identified as an attractive model for developmental studies due to its classical mosaic developmental pattern. Myosin heavy chain is a structural and functional component of myosin, the key muscle protein of thick filament. Here, full length cDNA of striated myosin heavy chains in C. gigas (CgSmhc) was obtained, and the expression profiles were examined in different development stage. CgSmhc had a high expression level in trochophore and D-shaped stage during embryo-larval stage. In adult, CgSmhc was a muscle-specific gene and primarily expressed in muscle tissues. Then, activity of 5' flanking region of CgSmhc were examined through an reconstructed EGFP vector. The results indicated that 3098 bp 5'-flanking region of CgSmhc owned various conserved binding sites of myogenesis-related regulatory elements, and the 2000 bp 5'-flanking sequence was sufficient to induce the CgSmhc expression. Subsequently, the CRISPR/Cas9-mediated target disruption of CgSmhc was generated by co-injection of Cas9mRNA and CgSmhc-sgRNAs into one-cell stage embryos of C. gigas. Loss of CgSmhc had a visible effect on the sarcomeric organization of thin filaments in larval musculature, indicating that CgSmhc was required during larval myogenesis to regulate the correct assembly of sarcomere.

Proteomic study of the brackish water mussel Mytilopsis leucophaeata

BACKGROUND

We encountered the opportunity to study proteochemically a brackish water invertebrate animal, Mytilopsis leucophaeata, belonging to the bivalves which stem from the second half of the Cambrian Period (about 510 million years ago). This way, we were able to compare it with the vertebrate animal, the frilled shark (Chlamydoselachus anguineus) that stems from a much later period of geologic time (Permian: 245-286 MYA).

RESULTS

The mussel contains a well-adapted system of protein synthesis on the ER, protein folding on the ER, protein trafficking via COPI or clathrin-coated vesicles from endoplasmic reticulum (ER) to Golgi and plasmalemma, an equally well-developed system of actin filaments that with myosin forms the transport system for vesicular proteins and tubulin, which is also involved in ATP-driven vesicular protein transport via microtubules or transport of chromosomes in mitosis and meiosis. A few of the systems that we could not detect in M. leucophaeata in comparison with C. anguineus are the synaptic vesicle cycle components as synaptobrevin, cellubrevin (v-snare) and synaptosomal associated protein 25-A (t-snare), although one component: Ras-related protein (O-Rab1) could be involved in synaptic vesicle traffic. Another component that we did not find in M. leucophaeata was Rab11 that is involved in the tubulovesicular recycling process of H+/K+-ATPase in C. anguineus. We have not been able to trace the H+/K+-ATPase of M. leucophaeata, but Na+/K+-ATPase was present. Furthermore, we have studied the increase of percent protein expression between 1,070 MYA (the generation of the Amoeba Dictyostelium discoideum) and present (the generation of the mammal Sus scrofa = wild boar). In this time span, three proteomic uprises did occur: 600 to 500 MYA, 47.5 to 4.75 MYA, and 1.4 to 0 MYA. The first uprise covers the generation of bivalves, the second covers gold fish, chicken, brine shrimp, house mouse, rabbit, Japanese medaka and Rattus norvegicus, and the third covers cow, chimpanzee, Homo sapiens, dog, goat, Puccinia graminis and wild boar. We hypothesise that the latter two uprises are related to geological and climate changes and their compensation in protein function expression.

CONCLUSIONS

The proteomic and evolutionary data demonstrate that M. leucophaeata is a highly educatioanal animal to study.

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Loss of filament-forming ability of myosin by non-enzymatic glycosylation and its molecular mechanism

Carp and scallop myosin and their subfragments (S-1 and rod) were reacted with glucose to investigate the effect of non-enzymatic glycosylation on the functionality of myosin. The filament-forming ability of the myosin rod diminished with the progress of non-enzymatic glycosylation and myosin became soluble in 0.1 M NaCl. The inhibition of the self-assembly of myosin molecules occurred chemically as a result of the increase in negative charge repulsion among myosin molecules and, further, physically as a result of the introduction of the glycosyl units into the surface of the rod region.

Proteolytic substructure of myorod, a thick filament protein of molluscan smooth muscles

Myorod (MR), a new thick filament protein of molluscan smooth muscles, is an alternatively spliced product of the myosin (Mn) heavy chain gene. We studied digestion of MR and Mn from the posterior adductor of Crenomytilus grayanus and the outer portion of adductor of Mizuchopecten (Patinopecten) yessoensis by papain and constructed the proteolytic substructure of MR, that is an analogue to Mn substructure. There are a head domain (analogue of Mn S1) and a rod domain (analogue of Mn rod); the junction between them is split at low ionic strength. The rod, in turn, consists of a neck domain (analogue of Mn S2) and a tail domain (identical to light meromyosin); the junction between them is split at high ionic strength. The localization and possible function of MR are discussed.

Solubility improvement of shellfish muscle proteins by reaction with glucose and its soluble state in low-ionic-strength medium

When myofibrillar proteins of scallop striated adductor muscle were reacted with glucose through the Maillard reaction, the change in the solubility of myofibrillar proteins in 0.05-0.5 M NaCl solutions during glycosylation and their soluble states were investigated. The solubility in low-ionic-strength media increased greatly with the progress of the Maillard reaction. The solubility in 0.1 M NaCl reached 83% when more than 60% of lysine residues in myofibrillar proteins were modified by glucose. However, the excess progress of the Maillard reaction impaired the improved solubility of myofibrillar proteins in a low-ionic-strength medium. Myosin, actin, and paramyosin in glycosylated myofibrillar proteins were solubilized independently regardless of NaCl concentration. In addition, the glycosylated myosin lost its filament-forming ability and existed as a monomer in 0.1 M NaCl.

Calcium-dependent structural changes in scallop heavy meromyosin

The mechanism of calcium regulation of scallop myosin is not understood, although it is known that both myosin heads are required. We have explored possible interactions between the heads of heavy meromyosin (HMM) in the presence and absence of calcium and nucleotides by sedimentation and electron microscope studies. The ATPase activity of the HMM preparation was activated over tenfold by calcium, indicating that the preparation contained mostly regulated molecules. In the presence of ADP or ATP analogs, calcium increased the asymmetry of the HMM molecule as judged by its slower sedimentation velocity compared with that in EGTA. In the absence of nucleotide the asymmetry was high even in EGTA. The shift in sedimentation occurred with a sharp midpoint at a calcium level of about 0.5 microM. Sedimentation of subfragment 1 was not dependent on calcium or on nucleotides. Modeling accounted for the observed sedimentation behavior by assuming that both HMM heads bent toward the tail in the absence of calcium, while in its presence the heads had random positions. The sedimentation pattern showed a single peak at all calcium concentrations, indicating equilibration between the two forms with a t(1/2) less than 70 seconds. Electron micrographs of crosslinked, rotary shadowed specimens indicated that 81 % of HMM molecules in the presence of nucleotide had both heads pointing back towards the tail in the absence of calcium, as compared with 41 % in its presence. This is consistent with the sedimentation data. We conclude that in the "off" state, scallop myosin heads interact with each other, forming a rigid structure with low ATPase activity. When molecules are switched "on" by binding of calcium, communication between the heads is lost, allowing them to flex randomly about the junction with the tail; this could facilitate their interaction with actin in contracting muscle.

Fluorescence measurements detect changes in scallop myosin regulatory domain

Ca2+-induced conformational changes of scallop myosin regulatory domain (RD) were studied using intrinsic fluorescence. Both the intensity and anisotropy of tryptophan fluorescence decreased significantly upon removal of Ca2+. By making a mutant RD we found that the Ca2+-induced fluorescence change is due mainly to Trp21 of the essential light chain which is located at the unusual Ca2+-binding EF-hand motif of the first domain. This result suggests that Trp21 is in a less hydrophobic and more flexible environment in the Ca2+-free state, supporting a model for regulation based on the 2 A resolution structure of scallop RD with bound Ca2+ [Houdusse A. and Cohen C. (1996) Structure 4, 21-32]. Binding of the fluorescent probe, 8-anilinonaphthalene-1-sulphonate (ANS) to the RD senses the dissociation of the regulatory light chain (RLC) in the presence of EDTA, by energy transfer from a tryptophan cluster (Trp818, 824, 826, 827) on the heavy chain (HC). We identified a hydrophobic pentapeptide (Leu836-Ala840) at the head-rod junction which is required for the effective energy transfer and conceivably is part of the ANS-binding site. Extension of the HC component of RD towards the rod region results in a larger ANS response, presumably indicating changes in HC-RLC interactions, which might be crucial for the regulatory function of scallop myosin.

Dimerization of the head-rod junction of scallop myosin

We have compared the dimerization properties and coiled-coil stability of various recombinant fragments of scallop myosin around the head-rod junction. The heavy-chain peptide of the regulatory domain and its various extensions toward the alpha-helical rod region were expressed in Escherichia coli, purified, and reconstituted with the light chains. Rod fragments of the same length but without the light-chain binding domain were also expressed. Electron micrographs show that the regulatory domain complex containing 340 residues of the rod forms dimers with two knobs (two regulatory domains) at one end attached to an approximately 50-nm coiled coil. These parallel dimers are in equilibrium with monomers (Kd = 10.6 microM). By contrast, complexes with shorter rod extensions remain predominantly monomeric. Dimers are present, accounting for ca. 5% of the molecules containing a rod fragment of 87 residues and ca. 30% of those with a 180-residue peptide. These dimers appear to be antiparallel coiled coils, as judged by their length and the knobs observed at the two ends. The rod fragments alone do not dimerize and form a coiled-coil structure unless covalently linked by disulfide bridges. Our results suggest that the N-terminal end of the coiled-coil rod is stabilized by interactions with the regulatory domain, most likely with residues of the regulatory light chain. This labile nature of the coiled coil at the head-rod junction might be a structural prerequisite for regulation of scallop myosin by Ca2+-ions.

A specific amino acid sequence at the head-rod junction is not critical for the phosphorylation-dependent regulation of smooth muscle myosin

It has been suggested that the structure at the head-rod junction of smooth muscle myosin is important for the phosphorylation-mediated regulation of myosin motor activity. To investigate whether a specific amino acid sequence at the head-rod junction is critical for the regulation, three smooth muscle myosin mutants in which the sequence at the N-terminal end of S2 is deleted to various extents were expressed in Sf9 cells; 28, 56, and 84 amino acid residues, respectively, at the position immediately C-terminal to the invariant proline (Pro849) were deleted, and the S1 domain was directly linked to the downstream sequence of the rod. The mutant myosins were expressed, purified, and biochemically characterized. All three myosin mutants showed a stable double-headed structure based upon electron microscopic observation. Both the actin-activated ATPase activity and the actin translocating activity of the mutants were completely regulated by the phosphorylation of the regulatory light chain. The actin sliding velocity of the three mutant myosins was the same as the wild-type recombinant myosin. These results indicate that a specific amino acid sequence at the head-rod junction is not required for the regulation of smooth muscle myosin. The results also suggest that there is no functionally important interaction between the regulatory light chain and the heavy chain at the head-rod junction.

Amino acid sequence of a Ca(2+)-transporting ATPase from the sarcoplasmic reticulum of the cross-striated part of the adductor muscle of the deep sea scallop: comparison to serca enzymes of other animals

The RT PCR approach was used to obtain the nucleotide sequence of the mRNA of a sarco/endoplasmic reticulum calcium transporting ATPase (SERCA) from the cross-striated (phasic) part of the adductor muscle of the deep sea scallop. Initially, degenerate primers based on consensus sequences among SERCAs and tryptic fragments of the scallop Ca-ATPase were used. The sequence was then extended using homologous primers and the 5' and 3' ends of the transcript determined by 5' and 3' RACE. The mRNA codes for a polypeptide chain 994 amino acid residues long (coded for by 2982 nucleotides) and has a 195 bp 5' untranslated region, with a 697 bp 3' untranslated region. The scallop enzyme shows strongest amino acid similarity to the SERCA enzyme of Loligo, followed by those of Drosophila and Artemia. It resembles the vertebrate SERCA3 in that it does not possess the phospholamban binding motif and so is unlikely to be regulated by protein kinase A mediated signals.

Molecular cloning and analysis of novel cDNAs specifically expressed in adult mouse testes

In an effort to examine the molecular basis of spermatogenesis, we isolated two types of novel cDNA clones specifically expressed in mouse testes. Type A cDNA (2,071 nucleotides) is predicted to encode 347 amino acid residues, whereas type B cDNA (1,536 nucleotides) has a deletion of 535 bp from nucleotides 1,206 to 1,740 of type A cDNA, probably due to alternative splicing. This deletion causes a frame shift of the putative open reading frame at the C-terminal portion of type A cDNA to encode 366 amino acid residues. Northern blot analysis using adult ICR organs demonstrated that both types of mRNAs were specifically expressed in testis, although type B mRNA was more abundant than type A mRNA. RT-PCR analysis revealed that these two mRNAs were also expressed in immature testes at 1, 5, 11, 16 and 24 days after birth. In situ hybridization analysis of adult ICR testes demonstrated that these two mRNAs were expressed in spermatogonia, Sertoli cells and Leydig cells. In the W/ WV mouse testis which lacks c-kit activity and spermatogonia, but contains Sertoli and Leydig cells, both mRNAs were found to be expressed in the latter two types of cells. We therefore termed these novel clones tsec-1, testis-specifically expressed cDNAs-1. The protein products of tsec-1 may play an important role in mammalian spermatogenesis.

Bi-directional movement of actin filaments along long bipolar tracks of oriented rabbit skeletal muscle myosin molecules

In actomyosin in vitro motility assays, orientation of myosin molecules affects their interaction with actin. We obtained long tracks of myosin molecules with uniform orientation. Bipolar filaments about 50 microm long were made from myosin rod prepared from molluscan smooth muscles, to which rabbit skeletal-muscle myosin bound, creating long synthetic thick-filaments. Movement of F-actin toward their center was much faster (4.7 +/- 0.6 microm s(-1)) than in the opposite direction (1.9 +/- 0.2 microm s(-1)), indicating that myosin molecules were arranged in the same orientation along each half of the bipolar filament. These complex thick-filaments permit measurement of actin movement over 20 microm of oriented skeletal myosin tracks facilitating mechanistic studies of actomyosin motility.

Essential and regulatory light chains of Placopecten striated and catch muscle myosins

ATPase activities of molluscan adductor muscle myosins show both muscle and species specific differences: ATPase activity of catch muscle myosin is lower than that of phasic muscle myosin; a 4-5-fold difference exists between the activities of phasic striated muscle myosins from the bay scallop (Argopecten irradians) and sea scallop (Placopecten magellanicus). To characterize the light chains of these myosins we determined the cDNA sequences of the essential light chains and the regulatory light chains from Placopecten striated and catch muscle. The nucleotide sequences of the essential light chains from Placopecten striated and catch muscle myosins are identical and show 94% identity and 98% homology to the Argopecten essential light chain indicating that the tissue and species specific differences in ATPase activities are not due to the essential light chain. We identified three regulatory light chain isoforms, one from striated and two from catch muscle. Sequence differences were restricted to nucleotides encoding some of the N-terminal 52 amino acids. The three recombinant Placopecten regulatory light chain isoforms and the Argopecten regulatory light chain were incorporated into hybrid myosins that contained the essential light chain and heavy chain from Placopecten striated, Placopecten catch, or Argopecten striated muscle. Measurement of the ATPase activities of these hybrids indicates clearly that it is the myosin heavy chain and not the regulatory light chains that are responsible for the muscle and species specific differences in enzymatic activities. Analysis of genomic DNA indicated that these regulatory light chain isoforms are products of a single regulatory light chain gene that is alternatively spliced in the 5' region only.

Sequence variations in the surface loop near the nucleotide binding site modulate the ATP turnover rates of molluscan myosins

The muscle and species-specific differences in enzymatic activity between Placopecten and Argopecten striated and catch muscle myosins are attributable to the myosin heavy chain. To identify sequences that may modulate these differences, we cloned and sequenced the cDNA encoding the myosin heavy chains of Placopecten striated and catch muscle. Deduced protein sequences indicate two similar isoforms in catch and striated myosins (97% identical); variations arise by differential RNA splicing of five alternative exons from a single myosin heavy chain gene. The first encodes the phosphate-binding loop; the second, part of the ATP binding site; the third, part of the actin binding site; the fourth, the hinge in the rod; and the fifth, a tailpiece found only in the catch muscle myosin heavy chain. Both Placopecten myosin heavy chains are 96% identical to Argopecten myosin heavy chaina isoforms. Because subfragment-1 ATPase activities reflect the differences observed in the parent myosins, the motor domain is responsible for the variations in ATPase activities. In addition, data show that differences are due to Vmax and not actin affinity. The sequences of all four myosin heavy chain motor domains diverge only in the flexible surface loop near the nucleotide binding pocket. Thus, the different ATPase activities of four molluscan muscle myosins are likely due to myosin heavy chain sequence variations within the flexible surface loop that forms part of the ATP binding pocket of the motor domain.

Regulation of contraction by calcium binding myosins

Contraction of molluscan muscles is triggered by binding of Ca2+ to myosin. Molluscan myosins are regulated molecules, their light chains serve as regulatory subunits. They differ from myosins of skeletal muscles in requiring Ca2+ for activity and having a specific high-affinity Ca2+ binding site. As all conventional myosins molluscan myosins also consist of two heavy chains, two regulatory and two essential light chains. Scallop myosin is particularly suitable for studying light chain function since its regulatory light chains readily dissociate in the absence of divalent cations and its essential light chains can be exchanged with foreign light chains. The structural, mutational and biochemical studies presented here are aimed to elucidate the role of the light chains in regulation, to describe the interactions between the myosin subunits and to locate the regions and the amino acids responsible for the differences between functional and non-functional light chains.

Essential light chain of Drosophila nonmuscle myosin II

We have cloned and sequenced a cDNA encoding the essential (alkaline) light chain of nonmuscle myosin from Drosophila melanogaster. The protein predicted from the cDNA matches partial amino acid sequence derived from essential light chain protein that copurifies with native nonmuscle myosin heavy chain. This completes the sequence of the three myosin subunits, two of which have been shown genetically to be required for morphogenesis and cytokinesis (the heavy chain encoded by zipper and the regulatory light chain encoded by spaghetti squash). The essential light chain protein is 147 amino acids in length and is 53% identical to human smooth muscle essential light chain. The sequence is consistent with the presence of four helix-loop-helix domains seen in crystallographic structures of the striated muscle myosin light chains and their close relative, calmodulin. We identified the most conserved residues among essential light chain sequences from multiple phyla and present their locations on the crystallographic structure of striated muscle essential light chain. This highlights several conserved contacts among the myosin subunits that may be important for the structure and regulation of the myosin motor. The gene encoding Drosophila nonmuscle essential light chain (Mlc-c) localizes to cytological position 5A6 and we discuss prospects for genetic analysis in this region.

Regulatory domains of myosins: influence of heavy chain on Ca(2+)-binding

Light chain binding domains of rabbit skeletal, turkey gizzard and scallop myosin comprised of equimolar amounts of a short heavy chain fragment, essential light chain, and regulatory light chain have been obtained following extensive tryptic digestion. These complexes that are analogous to the regulatory domain prepared previously from scallop myosin by digestion with clostripain resist proteolysis due to the mutual protection of the heavy chain and the light chains, and are common structural features of the myosins studied. Specific Ca(2+)-binding by the regulatory domains reflects the behaviour of intact myosin; only scallop regulatory domain has a specific Ca(2+)-binding site. The heavy chain fragments of the different regulatory domains have been isolated under denaturing conditions and reconstituted with scallop essential light chain and scallop regulatory light chain or turkey gizzard regulatory light chain to yield regulatory domain hybrids. Hybrids containing the turkey gizzard regulatory light chain were used in Ca(2+)-binding studies since they were far more stable than their counterparts with the scallop regulatory light chain. The gizzard hybrid binds Ca2+ with a comparable specificity but somewhat lower affinity than native scallop regulatory domain. The rabbit regulatory domain hybrid also binds Ca2+, although with a reduced affinity and specificity. The results indicate that Ca(2+)-binding ability is determined by the light chains and modified by the heavy chains.

Unconventional myosins

The unconventional myosins form a large and diverse group of molecular motors. The number of known unconventional myosins is increasing rapidly and in the past year alone two new classes have been identified. Substantial progress has been made towards characterizing the properties and functions of these motor proteins, which have been hypothesized to play fundamental roles in processes such as cell locomotion, phagocytosis and vesicle transport.