Location of the nonidentical two reactive lysine residues in the myosin molecule

Anti-TNP antibody localization of the reactive lysine residues in myosin

Myosin contains reactive lysine residues which are trinitrophenylated by 2,4,6-trinitrobenzene sulfonate much faster than the rest of the lysines. Here we find the location of these residues in the primary and spatial structure of myosin with the help of an anti-trinitrophenyl antibody. This antibody was raised against trinitrophenyl hemocyanin in rabbits. It reacted with trinitrophenylated myosin, and with some of the tryptic fragments of trinitrophenylated myosin. By analyzing the reaction with Western blots, it was found that the antibody preferentially reacts with the 27 kDa N-terminal fragment of the myosin head, and more weakly with the light meromyosin region of the myosin rod. The 27 kDa fragment contains the most reactive lysine residue, while the intermediate lysine residue is located in the light meromyosin region. The locations of the epitopes of the antibody were visualized on electron microscope images of rotary-shadowed trinitrophenylated myosin-antibody complexes. The distances of the epitopes to the head-rod junction of myosin were measured as 13 and 113 nm for the epitope on the head (reactive lysine residue) and for that on the rod (intermediary reactive lysine residue), respectively.

Localization of the ATP-binding site in the 23-kDa and 20-kDa regions of the heavy chain of the skeletal muscle myosin head

Three kinds of ATP analogues were synthesized. These ATP analogues can be classified into two conformations, i.e. syn and anti forms with respect to the N-glycosidic bond between adenine and ribose groups of ATP. 3'-O-(N-Methylanthraniloyl)-2-azidoadenosine 5'-triphosphate (MantN2(3)ATP) is recognized as the anti form, as ATP, and the other two, 3'-O-(N-methylanthraniloyl)-8-azidoadenosine 5'-triphosphate (MantN8(3)ATP) and 1,N6-etheno-8-azidoadenosine 5'-triphosphate (epsilon N8(3)ATP) are both syn forms. Mant and etheno groups are both fluorescent which allows detection of their binding to proteins. The photochemical binding of azido groups in ATP analogues to the myosin active site, examined in the presence and absence of ATP, showed that all the analogues bound to the site of myosin ATPase. These analogues also acted as substrates of the ATPase and were hydrolyzed in the active site, as judged by competitive inhibition of the ATPase and by their ATPase activities. Of these analogues, MantN2(3)ATP is very similar to ATP in divalent-cation dependence of its hydrolysis rate and in its ability to trap ADP in the active site with vanadate, while the other two are different from ATP in these respects. The photochemical binding sites of ATP analogues were localized by gel electrophoresis of trypsinized myosin ATPase with photocross-linked ATP analogues and/or by isolating the modified peptides. MantN2(3)ATP was found in the 23-kDa fragment which has a structure common to ATP-binding proteins, i.e. Gly-Xaa-Xaa-Gly-Xaa-Gly-Lys-Thr. Mant N8(3)ATP was found in a region of the 20-kDa fragment where actin is reported to attach.

The effect of pyrophosphate on the reaction of myosin with 2,4,6-trinitrobenzene sulphonate

Myosin was reacted with 2,4,6-trinitrobenzene sulphonate (TNBS) in the presence or absence of Mg-pyrophosphate. The reaction led to trinitrophenylation of lysyl residues which could be divided on the basis of the reaction into three classes: (i) two rapidly reacting lysyl residues (RLR), one residing on each head of myosin, whose rate of reaction depends on the presence of Mg-pyrophosphate; (ii) two lysyl residues which react with intermediate rate (ILR) and reside on the rod segment of myosin; and (iii) the remaining lysyl residues of myosin which react slowly with TNBS. The rate of the trinitrophenylation of RLR was followed spectrophotometrically and enzymatically, measuring an absorbance change at 345 nm, and also changes in K+ (EDTA)-, Mg2+- and Ca2+-activated ATPase activities, respectively. According to analysis of the kinetics of the reaction, Mg-pyrophosphate inhibited the rate of trinitrophenylation in both heads of myosin, not in one head only as was suggested by Miyanishi et al. (J. Biochem Tokyo 85; 1979). Myosin heads (myosin subfragment-1, S-1) were prepared by digesting myosin trinitrophenylated in the absence and presence of Mg-pyrophosphate with chymotrypsin. S-1, with trinitrophenylated RLR, was separated from non-trinitrophenylated S-1 by DEAE cellulose column chromatography. The trinitrophenylated S-1 had a high Mg2+- and a low K+(EDTA)-activated ATPase while the non-trinitrophenylated species had the usual high K+(EDTA)- and low Mg2+-ATPase activity. This results excluded the possibility suggested by Miyanishi et al., that the myosin head, which is resistant to trinitrophenylation in the presence of Mg-pyrophosphate, did not possess K+(EDTA)-activated ATPase activity. The presence of Mg-pyrophosphate during trinitrophenylation substantially affected the enzymic characteristics of the modified myosin. The myosin trinitrophenylated in the presence of Mg-pyrophosphate had a higher K+(EDTA)- and a lower Mg2+-ATPase activity. SH1 (Cys-707) also probably becomes a target of the reaction if myosin is trinitrophenylated in the presence of Mg-pyrophosphate. This is deduced from the following findings: (i) the addition of dithiothreitol after trinitrophenylation partially reversed the loss in the K+(EDTA)-ATPase activity; and (ii) the specific alkylation of the SH1 thiol by 1,5-IAEDANS prior to trinitrophenylation prevented the effect of dithiothreitol on the ATPase activity of myosin. The results indicated that Mg-pyrophosphate induced structural changes in the myosin molecule which influenced the course and possibly the target(s) of trinitrophenylation.

Molecular movements promoted by metal nucleotides in the heavy-chain regions of myosin heads from skeletal muscle

Molecular movements generated in the heavy-chain regions (27-50-20(X 10(3)) Mr) of myosin S1 on interaction with nucleotides ATP, AMPPNP, ADP and PPi were investigated by limited proteolysis of several enzyme-metal nucleotide complexes in the absence and presence of reversibly bound and crosslinked F-actin. The rate and extent of the nucleotide-promoted conversion of the NH2-terminal 27 X 10(3) Mr and 50 X 10(3) Mr segments into products of 22 X 10(3) Mr and 45 X 10(3) Mr, respectively, were estimated to determine the amplitude of the molecular movements. The 22 X 10(3) Mr peptide was identified by amino acid sequence studies as being derived from cleavage of the peptide bond between Arg and Ile (at position 23 to 24). The 45 X 10(3) Mr peptide, previously shown to represent the NH2-terminal part of the 50 X 10(3) Mr region, would be connected to the adjacent C-terminal 20 X 10(3) Mr region by a pre-existing loop segment of about 5 X 10(3) Mr; the proteolytic sensitivity of the latter region is increased particularly by nucleotide binding. The tryptic reaction proved to be a sensitive indicator of the conformational state of the liganded heavy chain as the rate of peptide bond cleavage in the two regions is dependent on the nature of the bound ligand; it decreases in the order: ATP greater than AMPPNP greater than ADP greater than PPi. It depends also on the nature of the metal present, Mg2+ and Ca2+ being much more effective than K+. Binding of F-actin to the S1-MgAMPPNP complex affords significant protection against breakdown of 27 X 10(3) Mr and 50 X 10(3) Mr peptides, but with concomitant hydrolysis of the 50 X 10(3) Mr-20 X 10(3) Mr junction. Additionally, interaction of MgATP with HMM modulates the tryptic fission of the S1-S2 region. The overall data provide a molecular support for the two-state model of the myosin head and emphasize the involvement of the 50 X 10(3) Mr unit in the mechanism of coupling between the actin and nucleotide binding sites.

Trinitrophenylation of smooth muscle myosin

The reaction of trinitrobenzenesulfonate with gizzard myosin was studied. The initial phase of the reaction involved two residues and at this level of modification the following was observed: the Mg2+-ATPase of myosin, the actin-activated ATPase of phosphorylated myosin and the phosphorylation kinetics of myosin were not affected. However, trinitrophenylation did induce an activation of the actin-activated ATPase of dephosphorylated myosin and in this respect mimicked the effect of light chain phosphorylation. The Mg2+-dependence of actin-activated ATPase also is altered on trinitrophenylation. These alterations of enzymatic properties could be at least partly explained by the finding that trinitrophenylation favored the 6S conformation of myosin.

Functionality of muscle proteins in gelation mechanisms of structured meat products

Recent advances in muscle biology concerning the discoveries of a large variety of proteins have been described in this review. The existence of polymorphism in several muscle proteins is now well established. Various isoforms of myosin not only account for the difference in physiological functions and biochemical activity of different fiber types or muscles, but also seem to differ in functional properties in food systems. The functionality of various muscle proteins, especially myosin and actin in the gelation process in modal systems which simulate structured meat products, is discussed at length. Besides, the role of different subunits and subfragments of myosin molecule in the gelation mechanism, and the various factors affecting heat-induced gelation of actomyosin in modal systems are also highlighted. Finally, the areas which need further investigation in this discipline have been suggested.