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H Brzeska

Publications and source records attributed to H Brzeska.

35 records · Page 2Linked to original sources
PubMed1990

Substrate specificity of Acanthamoeba myosin I heavy chain kinase as determined with synthetic peptides.

Phosphorylation of a single threonine (myosin IA) or serine (myosins IB and IC) in the heavy chains of the Acanthamoeba myosin I isozymes is required for expression of their actin-activated Mg2(+)-ATPase activities. We now report that the synthetic peptide Gly-Arg-Gly-Arg-Ser-Ser-Val-Tyr-Ser, which corresponds to the phosphorylated region of Acanthamoeba myosin IC, is a good substrate for myosin I heavy chain kinase: Km = 54 microM, and Vmax = 15 mumols/min.mg. The same serine is phosphorylated as in the native substrate (residue 6 in the above sequence), and kinase activity with the synthetic peptide as substrate is also stimulated by phosphatidylserine-enhanced autophosphorylation of the kinase. These results indicate that all of the essential sequence determinants of kinase specificity are contained within this 9-residue peptide. With the peptide as substrate, we found that another acidic phospholipid, phosphatidylinositol, also enhances autophosphorylation of the kinase whereas the neutral phospholipids phosphatidylcholine and phosphatidylethanolamine do not. By comparing the Km and Vmax values for a series of synthetic peptide substrates, we established that 1 basic amino acid is essential on the NH2-terminal side of the phosphorylation site, and two are preferable, and that a tyrosine is essential 2 residues away on the COOH-terminal side. There is a slight preference for arginines over lysines. All of these local sequence specificity determinants are present in the three native substrates, Acanthamoeba myosins IA, IB, and IC, and in two Dictyostelium myosin I isozymes that are putative substrates for the kinase. Similar sequences do not occur in the myosins I from intestinal brush border, which is not a substrate for the Acanthamoeba kinase.

Acanthamoeba↗
PubMed1990

Acanthamoeba myosin I heavy chain kinase is activated by phosphatidylserine-enhanced phosphorylation.

The actin-activated Mg2(+)-ATPase activities of myosins I from Acanthamoeba castellanii are fully expressed only when a single amino acid on their heavy chain is phosphorylated by myosin I heavy chain kinase. Here we show that kinase isolated by a procedure designed to minimize its phosphorylation during purification can incorporate up to 7.5 mol of phosphate/mol of enzyme when incubated with ATP, possibly by autophosphorylation. The rate of phosphorylation is enhanced about 20-fold by phosphatidylserine but is unaffected by calcium ions. Phosphorylation increases the rate at which the kinase phosphorylates the regulatory site of myosin I by about 50-fold. These results suggest that (auto?)phosphorylation may regulate the activity of myosin I heavy chain kinase in vivo. The stimulation of kinase phosphorylation by phosphatidylserine (other phospholipids have not yet been tested) is of particular interest because myosin I has been shown to be tightly associated with membranes, especially the plasma membrane.

Acanthamoeba↗
PubMed1989

Purification and characterization of a third isoform of myosin I from Acanthamoeba castellanii.

A third isoform of myosin I has been isolated from Acanthamoeba and designated myosin IC. Peptide maps and immunoassays indicate that myosin IC is not a modified form of myosin IA, IB, or II. However, myosin IC has most of the distinctive properties of a myosin I. It is a globular protein of native Mr approximately 162,000, apparently composed of a single 130-kDa heavy chain and a pair of 14-kDa light chains. It is soluble in MgATP at low ionic strength, conditions favoring filament assembly by myosin II. Myosin IC has high Ca2+- and (K+,EDTA)-ATPase activities. Its low Mg2+-ATPase activity is stimulated to a maximum rate of 20 s-1 by the addition of F-actin if its heavy chain has been phosphorylated by myosin I heavy chain kinase. The dependence of the Mg2+-ATPase activity of myosin IC on F-actin concentration is triphasic; and, at fixed concentrations of F-action, this activity increases cooperatively as the concentration of myosin IC is increased. These unusual kinetics were first demonstrated for myosins IA and IB and shown to be due to the presence of two actin-binding sites on each heavy chain which enable those myosins I to cross-link actin filaments. Myosin IC is also capable of cross-linking F-actin, which, together with the kinetics of its actin-activated Mg2+-ATPase activity, suggests that it, like myosins IA and IB, possesses two independent actin-binding domains.

Acanthamoeba↗
PubMed1989

The localization and sequence of the phosphorylation sites of Acanthamoeba myosins I. An improved method for locating the phosphorylated amino acid.

The actin-activated Mg2+-ATPase activities of Acanthamoeba myosins IA, IB, and IC are expressed only when a single site in their heavy chains is phosphorylated by a myosin I heavy chain-specific kinase. We show that phosphorylation occurs at Ser-315 in the myosin IB heavy chain, Ser-311 in myosin IC, and a threonine residue at a corresponding position in myosin IA whose amino acid sequence is as yet unknown. The most obvious feature common to the three substrates is a basic amino acid(s) 2 or 3 residues before the site of phosphorylation. The phosphorylation site is located between the ATP- and actin-binding sites, which corresponds to the middle of the 50-kDa domain of skeletal muscle myosin subfragment 1. The sequence similarity between the region surrounding the phosphorylation site of myosin I and subfragment 1 is much lower than the average sequence similarity between myosin I and subfragment 1. This is consistent with the hypothesis that the conformation of this region of myosin I differs from that of the corresponding region in skeletal muscle myosin and that phosphorylation converts the conformation of the actomyosin I complex into a conformation comparable to that present in actosubfragment 1 without phosphorylation. The protein sequences obtained in the course of this work led to the conclusion that the myosin I genes previously identified as myosin IB and IL (myosin-like) heavy chains actually are the myosin IC and IB heavy chains, respectively. Finally, we report a modification of the method for monitoring the appearance of 32Pi during sequencing of 32P-labeled peptides that results in almost complete recovery of the radioactivity, thus allowing unequivocal assignment of the position of the phosphorylated residue.

Acanthamoeba↗
PubMed1989

Myosin I is located at the leading edges of locomoting Dictyostelium amoebae.

Movement of a eukaryotic cell along a substrate occurs by extension of lamellipodia and pseudopodia at the anterior and retraction at the posterior of the cell. The molecular and structural mechanisms of these movements are uncertain. Dictyostelium discoideum contains two forms of myosin. Here we show by immunofluorescence microscopy that non-filamentous myosin I occurs at the leading edges of the lamellipodial projections of migrating Dictyostelium amoebae, which are devoid of myosin II, whereas filamentous myosin II is concentrated in the posterior of the cells. On the basis of these locations of the two forms of myosin and their known biochemical and biophysical properties, we suggest that actomyosin I may contribute to the forces that cause extension at the leading edge of a motile cell, while the contraction of actomyosin II at the rear squeezes the cell mass forward. Myosin I isozymes might have similar roles in metazoan cells, for example at the leading edges of neuronal growth cones, and in the extension of lamellipodia and pseudopodia of leukocytes, macrophages and fibroblasts.

Cell Movement↗
PubMed1989

The effect of actin and phosphorylation on the tryptic cleavage pattern of Acanthamoeba myosin IA.

The Mg2+-ATPase activity of Acanthamoeba myosin IA is activated by F-actin only when the myosin heavy chain is phosphorylated at a single residue. In order to gain insight into the conformational changes that may be responsible for the effects of F-actin and phosphorylation on myosin I ATPase, we have studied their effects on the proteolysis of the myosin IA heavy chain by trypsin. Trypsin initially cleaves the unphosphorylated, 140-kDa heavy chain of Acanthamoeba myosin IA at sites 38 and 112 kDa from its NH2 terminus and secondarily at sites 64 and 91 kDa from the NH2 terminus. F-actin has no effect on tryptic cleavage at the 91- and 112-kDa sites, but does protect the 38-kDa site and the 64-kDa site. Phosphorylation (which occurs very near the 38-kDa site) has no detectable effect on the tryptic cleavage pattern in the absence of F-actin or on F-actin protection of the 64-kDa site, but significantly enhances F-actin protection of the 38-kDa site. Protection of the 64-kDa site is probably due to direct steric blocking because F-actin binds to this region of the heavy chain. The protection of the 38-kDa site by F-actin may be the result of conformational changes in this region of the heavy chain induced by F-actin binding near the 64-kDa site and by phosphorylation. The conformational changes in the heavy chain of myosin IA that are detected by alterations in its susceptibility to proteolysis are likely to be related to the conformational changes that are involved in the phosphorylation-regulated actin-activated Mg2+-ATPase activities of Acanthamoeba myosins IA and IB.

Acanthamoeba↗
PubMed1988

Localization of the actin-binding sites of Acanthamoeba myosin IB and effect of limited proteolysis on its actin-activated Mg2+-ATPase activity.

Acanthamoeba myosin IB contains a 125-kDa heavy chain that has high actin-activated Mg2+-ATPase activity when 1 serine residue is phosphorylated. The heavy chain contains two F-actin-binding sites, one associated with the catalytic site and a second which allows myosin IB to cross-link actin filaments but has no direct effect on catalytic activity. Tryptic digestion of the heavy chain initially produces an NH2-terminal 62-kDa peptide that contains the ATP-binding site and the regulatory phosphorylation site, and a COOH-terminal 68-kDa peptide. F-actin, in the absence of ATP, protects this site and tryptic cleavage then produces an NH2-terminal 80-kDa peptide. Both the 62- and the 80-kDa peptides retain the (NH+4,EDTA)-ATPase activity of native myosin IB and both bind to F-actin in an ATP-sensitive manner. However, only the 80-kDa peptide retains a major portion of the actin-activated Mg2+-ATPase activity. This activity requires phosphorylation of the 80-kDa peptide by myosin I heavy chain kinase but, in contrast to the activity of intact myosin IB, it has a simple, hyperbolic dependence on the concentration of F-actin. Also unlike myosin IB, the 80-kDa peptide cannot cross-link F-actin filaments indicating the presence of only a single actin-binding site. These results allow the assignment of the actin-binding site involved in catalytic activity to the region near, and possibly on both sides of, the tryptic cleavage site 62 kDa from the NH2 terminus, and the second actin-binding site to the COOH-terminal 45-kDa domain. Thus, the NH2-terminal 80 kDa of the myosin IB heavy chain is functionally similar to the 93-kDa subfragment 1 of muscle myosin and most likely has a similar organization of functional domains.

Acanthamoeba↗
PubMed1988

Structure-function studies on Acanthamoeba myosins IA, IB, and II.

Myosins IA and IB are globular proteins with only a single, short (for myosins) heavy chain (140,000 and 125,000 daltons for IA and IB, respectively) and are unable to form bipolar filaments. The amino acid sequence of IB heavy chain shows 55% similarity to muscle myosins in the N-terminal 670 residues, which contain the active sites, and a unique 500-residue C-terminus highly enriched in proline, glycine, and alanine. The C-terminal region contains a second actin-binding site which allows myosins IA and IB to cross-link actin filaments and support contractile activity. Myosins IA and IB are regulated solely by phosphorylation of one serine on the heavy chain positioned between the catalytic site and the actin-binding site that activates ATPase. Myosin II is a more conventional myosin in composition (two heavy chains and two pairs of light chains), heavy chain sequence (globular head 45% identical to muscle myosins and a coiled-coil helical tail), and structure (bipolar filaments). The tail of myosin II is much shorter than that of other conventional myosins, and it contains a 25 amino acid sequence in which helical structure is predicted to be weak or absent. The position of this sequence corresponds to the position of a bend in the monomer. Myosin II heavy chains also have a 29-residue nonhelical tailpiece which contains three regulatory, phosphorylatable serines. Phosphorylation at the tip of the tail regulates ATPase activity in the globular head apparently through an effect on filament structure.

Acanthamoeba↗
PubMed1987

Limited tryptic digestion of Acanthamoeba myosin IA abolishes regulation of actin-activated ATPase activity by heavy chain phosphorylation.

Acanthamoeba myosin IA is a globular protein composed of a 140-kDa heavy chain and a 17-kDa light chain. It expresses high actin-activated Mg2+-ATPase activity when one serine on the heavy chain is phosphorylated. We previously showed that chymotrypsin cleaves the heavy chain into a COOH-terminal 27-kDa peptide that can bind to F-actin but has no ATPase activity and a complex containing the NH2-terminal 112-kDa peptide and the light chain. The complex also binds F-actin and has full actin-activated Mg2+-ATPase activity when the regulatory site is phosphorylated. We have now localized the ATP binding site to within 27 kDa of the NH2 terminus and the regulatory phosphorylatable serine to a 20-kDa region between 38 and 58 kDa of the NH2 terminus. Under controlled conditions, trypsin cleaves the heavy chain at two sites, 38 and 112 kDa from the NH2 terminus, producing a COOH-terminal 27-kDa peptide similar to that produced by chymotrypsin and a complex consisting of an NH2-terminal kDa peptide, a central 74-kDa peptide, and the light chain. This complex is similar to the chymotryptic complex but for the cleavage which separates the 38- and 74-kDa peptides. The tryptic complex has full (K+, EDTA)-ATPase activity (the catalytic site is functional) and normal ATP-sensitive actin-binding properties. However, the actin-activated Mg2+-ATPase activity and the F-actin-binding characteristics of the tryptic complex are no longer sensitive to phosphorylation of the regulatory serine. Therefore, cleavage between the phosphorylation site and the ATP-binding site inhibits the effects of phosphorylation on actin binding and actin-activated Mg2+-ATPase activity without abolishing the interactions between the ATP- and actin-binding sites.

Acanthamoeba↗
PubMed1986

Interaction of calmodulin and its fragments with Ca2+-ATPase and myosin light chain kinase.

The binding of smooth muscle myosin light chain kinase (MLCK) and erythrocyte membrane Ca2+-ATPase to calmodulin (CM), or calmodulin fragments was investigated using CM-, or CM fragment-affinity column chromatography. Calmodulin fragments corresponding to amino acid residues 1-77 (TR1-C), 78-148 (TR2-C) and 107-148 (TR3-E) were used. The ability of calmodulin fragments to activate these enzymes was also studied. Fragments TR1-C and TR2-C were able to bind to Ca2+-ATPase but only TR2-C stimulated its activity. Only the TR2-C fragment bound MLCK but failed to activate this enzyme at the molar excess sufficient for activation of Ca2+-ATPase. These results suggest a different mode of calmodulin interaction with Ca2+-ATPase and MLCK.

Animals↗
PubMed1986

Characterization of a calmodulin antiserum by its reactions with fragments of the calmodulin molecule.

A high affinity antibody, specific to the calcium-free form of calmodulin, which had previously been developed using N-acetyl-muramyl-L-alanyl-D-isoglutamine-calmodulin conjugate as an immunogen, was tested for cross-reactivity with tryptic fragments of calmodulin (CaM1-77, CaM1-90, CaM78-149, and CaM106-149) as well as with synthetic peptides corresponding to the 1st, 2nd, and 3rd calcium binding loop of calmodulin. The results showed that the antigenic determinant involves a special conformation of amino acid residues 90-106 in the 3rd calcium-binding domain.

Antibody Specificity↗
PubMed1983

Localization of hydrophobic sites in calmodulin and skeletal muscle troponin C studied using tryptic fragments: a simple method of their preparation.

The exposure of hydrophobic sites on calmodulin, skeletal muscle troponin C and their tryptic fragments was investigated using Phenyl-Sepharose chromatography. A strong binding of both proteins and their fragments corresponding to the NH2-terminal halves of polypeptide chain of respective proteins in the presence of calcium ions was observed. Only a weak interaction with Phenyl-Sepharose or its lack was observed under these conditions for fragments corresponding to the COOH-terminal halves of calmodulin and troponin C, respectively. The elution of the samples from Phenyl-Sepharose column with ethylene glycol gradient allowed to compare relative hydrophobicity of both proteins and their fragments. The results show that hydrophobic properties of calmodulin and troponin C are virtually preserved in their fragments obtained as a result of their cleavage by trypsin in half. They also indicated that the exposure of hydrophobic residues caused by the binding of calcium ions takes place mainly in the NH2-terminal halves of polypeptide chains of both proteins. A simple method of purification of tryptic fragments of both proteins based on the difference in the strength of their interactions with Phenyl-Sepharose is described.

Animals↗
PubMed1980

Sodium-23 nuclear magnetic resonance as an indicator of sodium binding to calmodulin and tryptic fragments, in relation to calcium content.

The relaxation rate enhancements of the 23Na nuclei for NaHCO3 solutions of calmodulin and its tryptic peptides TR-1 and TR-2 indicate true binding of Na+ ions to these biomolecules. With both TR-1 and TR-2, Na+ binding occurs in competition with Ca2+ and Mg2+ binding: log KNa approximately equal to 2, log KMg apoproximately equal to 4, log KCa approximately equal to 6 for TR-1; and log KNa approximately equal to 2, log KMg approximately equal to 3, log KCa approximately equal to 5 for TR-2. All the binding constants are systemically greater for binding to TR-1, as compared to TR-2. There is also an increase in KNa for TR-1 of calmodulin as compared to the homologous tryptic fragment of troponin C. The increased binding is identified tentatively with site I of calmodulin. The binding constants KNa, KCa and KMg of calmodulin appear to be finely tuned to the intracellular concentrations of these cations.

Animals↗