On the presence of calmodulin-like protein in mycobacteria

EF-hand protein, EfhP, specifically binds Ca2+ and mediates Ca2+ regulation of virulence in a human pathogen Pseudomonas aeruginosa

Calcium (Ca2+) is well known as a second messenger in eukaryotes, where Ca2+ signaling controls life-sustaining cellular processes. Although bacteria produce the components required for Ca2+ signaling, little is known about the mechanisms of bacterial Ca2+ signaling. Previously, we have identified a putative Ca2+-binding protein EfhP (PA4107) with two canonical EF-hand motifs and reported that EfhP mediates Ca2+ regulation of virulence factors production and infectivity in Pseudomonas aeruginosa, a human pathogen causing life-threatening infections. Here, we show that EfhP selectively binds Ca2+ with 13.7 µM affinity, and that mutations at the +X and -Z positions within each or both EF-hand motifs abolished Ca2+ binding. We also show that the hydrophobicity of EfhP increased in a Ca2+-dependent manner, however no such response was detected in the mutated proteins. 15 N-NMR showed Ca2+-dependent chemical shifts in EfhP confirming Ca2+-binding triggered structural rearrangements in the protein. Deletion of efhP impaired P. aeruginosa survival in macrophages and virulence in vivo. Disabling EfhP Ca2+ binding abolished Ca2+ induction of pyocyanin production in vitro. These data confirm that EfhP selectively binds Ca2+, which triggers its structural changes required for the Ca2+ regulation of P. aeruginosa virulence, thus establishing the role of EfhP as a Ca2+ sensor.

Calcium Regulation of Bacterial Virulence

Calcium (Ca²⁺) is a universal signaling ion, whose major informational role shaped the evolution of signaling pathways, enabling cellular communications and responsiveness to both the intracellular and extracellular environments. Elaborate Ca²⁺ regulatory networks have been well characterized in eukaryotic cells, where Ca²⁺ regulates a number of essential cellular processes, ranging from cell division, transport and motility, to apoptosis and pathogenesis. However, in bacteria, the knowledge on Ca²⁺ signaling is still fragmentary. This is complicated by the large variability of environments that bacteria inhabit with diverse levels of Ca²⁺. Yet another complication arises when bacterial pathogens invade a host and become exposed to different levels of Ca²⁺ that (1) are tightly regulated by the host, (2) control host defenses including immune responses to bacterial infections, and (3) become impaired during diseases. The invading pathogens evolved to recognize and respond to the host Ca²⁺, triggering the molecular mechanisms of adhesion, biofilm formation, host cellular damage, and host-defense resistance, processes enabling the development of persistent infections. In this review, we discuss: (1) Ca²⁺ as a determinant of a host environment for invading bacterial pathogens, (2) the role of Ca²⁺ in regulating main events of host colonization and bacterial virulence, and (3) the molecular mechanisms of Ca²⁺ signaling in bacterial pathogens.

Calmodulin-like protein from M. tuberculosis H37Rv is required during infection

M. tuberculosis constitutes very sophisticated signaling systems that convert the environment signals into appropriate cellular response and helps the bacilli to overcome the onslaught of host defence mechanisms. Although mycobacterial two-component systems and STPKs have gained lot of attention as virulence factors, mycobacterial calcium signaling has not been very well studied. Calcium signaling has been the primary mechanism in eukaryotes for regulation of kinases, however in prokaryotes auto-phosphorylation of number of kinases has been reported. We have previously reported a small calmodulin-like-protein (CAMLP) from M. tuberculosis regulating enzymes of heterogeneous origin. To understand its role in both viability and virulence, we have assessed the effect of reduced expression of CAMLP coding gene Rv1211 on M. tb growth in vitro and ex vivo. Further, we have also studied the expression profile of Rv1211 in various conditions simulating host microenvironments. Our results highlight the possible role of CAMLP in growth and survival of M. tb during infection.

Cloning and expression of the gene for a novel protein from Mycobacterium smegmatis with functional similarity to eukaryotic calmodulin

A calmodulin-like protein (CAMLP) from Mycobacterium smegmatis was purified to homogeneity and partially sequenced; these data were used to produce a full-length clone, whose DNA sequence contained a 55-amino-acid open reading frame. M. smegmatis CAMLP, expressed in Escherichia coli, exhibited properties characteristic of eukaryotic calmodulin: calcium-dependent stimulation of eukaryotic phosphodiesterase, which was inhibited by the calmodulin antagonist trifluoperazine, and reaction with anti-bovine brain calmodulin antibodies. Consistent with the presence of nine acidic amino acids (16%) in M. smegmatis CAMLP, there is one putative calcium-binding domain in this CAMLP, compared to four such domains for eukaryotic calmodulin, reflecting the smaller molecular size (approximately 6 kDa) of M. smegmatis CAMLP. Ultracentrifugation and mass spectral studies excluded the possibility that calcium promotes oligomerization of purified M. smegmatis CAMLP.

Immunocytochemical localization of a calmodulinlike protein in Bacillus subtilis cells

To determine possible functions of the calmodulinlike protein of Bacillus subtilis, the time course of its expression during sporulation and its cellular localization were studied. The protein was expressed in a constitutive manner from the end of logarithmic growth through 8 h of sporulation as determined by antibody cross-reactivity immunoblots and enzyme-linked immunosorbent assays (ELISAs). In partially purified extracts, the immunopositive protein comigrated upon electrophoresis with a protein which selectively bound [(45)Ca]CaCl(2), ruthenium red, and Stains-all. Previous studies showed increased extractability of the calmodulinlike protein from B. subtilis cells when urea and 2-mercaptoethanol were used in breakage buffers, implying that the protein might be partially associated with the membrane fraction. This was confirmed by demonstrating that isolated membrane vesicles of B. subtilis also gave positive immunological tests with Western blotting and ELISAs. To more precisely locate the protein in cells, thin sections of late-log-phase cells, sporulating cells, and free spores were reacted first with bovine brain anticalmodulin specific antibodies and then with gold-conjugated secondary antibodies; the thin sections were examined by transmission electron microscopy. The calmodulinlike protein was found almost exclusively associated with the cell envelope of these fixed, sectioned cells. A possible function of the calmodulinlike protein in sensing calcium ions or regulating calcium ion transport is suggested.

Effect of trifluoperazine on in vitro ATP synthesis by Mycobacterium leprae

The effect of trifluoperazine (TFP), a calmodulin antagonist, was investigated on in vitro ATP levels of human derived Mycobacterium leprae. M. leprae were obtained from biopsies from multi-bacillary forms of leprosy and were incubated in a modified Dubos medium system which supports limited in vitro synthesis of M. leprae. This incubation was carried out in the absence and presence of different concentrations of trifluoperazine. Samples for estimation of bacillary ATP levels were taken at day 0 and at 14 days of incubation. TFP inhibited ATP levels in M. leprae and this inhibitory effect was marginal at 2.5 microg ml(-1) (35% inhibition), highly significant at 5 microg ml(-1) (87% inhibition) and almost total at 10 microg ml(-1) (98.5% inhibition). This compound appears to have potential as an anti-leprotic drug and also as a broad spectrum anti-mycobacterial agent in view of its anti-tubercular activity reported earlier.

Isolation, purification and characterization of intracellular calmodulin like protein (CALP) from Mycobacterium phlei

A monomeric acidic protein of 14,000 Da with an isoelectric point of 4.5 was isolated from Mycobacterium phlei, which stained poorly with Coomassie brilliant blue. This protein showed retardation in mobility in SDS-PAGE upon treatment with calcium, similar to eukaryotic calmodulin proteins. Activation of cAMP phosphodiesterase and NAD kinase by this protein was observed. The CD spectral analysis indicated that the CALP has 52% of beta-conformation. The regular beta-conformation of the calmodulin like protein was shifted to 46% alpha-helical structure when calcium ions reacted with the protein, however, 42% of the CALP still retained its original beta-conformation. These observations indicated homology of this calcium binding protein with that of eukaryotic calmodulins in few structural and functional properties.

Identification, localization and possible role of calmodulin like protein in phospholipid synthesis of Microsporum gypseum

Calmodulin like protein has been identified for the first time in dermatophyte--M. gypseum (by specific radioimmunoassay). Maximum amount of this protein was present in the early and mid log phase of growth and was mainly localized in the cytosolic fraction. Cells treated or grown with calmodulin antagonists (phenothiazine and trifluoperazine) exhibited lower uptake of [14C]acetate or labelled phosphate into phospholipids. This is probably due to lower levels of calmodulin seen in these cells. Our results suggest the relationship between calmodulin levels and phospholipid synthesis in Microsporum gypseum.

Possible role of calcium in phospholipid synthesis of Microsporum gypseum

The effect of calcium on lipid synthesis in Microsporum gypseum was examined by growing these cells in calcium supplemented (1 mM to 10 mM) medium. Maximum incorporation of [14C]acetate into total lipids and phospholipids was observed in cells grown with 6 mM calcium. This was probably due to a 3-fold increase in total calcium levels as incorporation of label was inhibited in total lipids (33%) and phospholipids (20.5%) in calcium-grown cells which were preincubated with the calcium specific chelator ethylene glycolbis (beta-aminoethyl ester) N,N,N',N',-tetracetate (EGTA). Increased incorporation of [14C]acetate into phospholipids was further supported by increase in the activity of key phospholipid biosynthetic enzymes (glycerolkinase and glycerol-3-phosphate acyltransferase) as well as the increase in phospholipid content in calcium-grown cells, which suggests a correlation between increased calcium levels and phospholipid biosynthesis in M. gypseum.

Purification and characterization of Bordetella calmodulin-like protein

Bordetella calmodulin-like protein was purified from culture supernatant fluid of B. pertussis, B. parapertussis and B. bronchiseptica by successive chromatography on hydroxyapatite, Toyopearl HW-50F and QAE-Toyopearl 550C columns. The purified calmodulin-like protein appeared to be homogeneous by SDS-polyacrylamide gel electrophoresis. The apparent molecular mass of calmodulin-like protein on SDS-polyacrylamide gel electrophoresis was 10 kDa, which was smaller than bovine brain calmodulin (17 kDa). The purified calmodulin-like protein activated both Bordetella adenylate cyclase and mammalian phosphodiesterase in a Ca(2+)-dependent manner. This activation was inhibited by calmodulin antagonists. The calmodulin-like protein, like calmodulin, was retained by a hydrophobic resin in the presence of Ca2+ and eluted by the addition of EDTA. These results indicated that the Bordetella calmodulin-like protein is closely related to calmodulin. As a putative calmodulin the extracellular calmodulin may be involved in Bordetella pathogenesis.

Trifluoperazine inhibits the incorporation of labelled precursors into lipids, proteins and DNA of Mycobacterium tuberculosis H37Rv

We have recently demonstrated that the calmodulin antagonist trifluoperazine has antitubercular activity in vitro against Mycobacterium tuberculosis H37Rv susceptible and resistant to isoniazid. It is now shown that trifluoperazine at a concentration of 50 micrograms ml-1 when added to the cells along with the labelled precursors inhibited the incorporation of [14C]acetate into lipids (63%) and uptake of [14C]glycine (74%) and [3H]thymidine (52%) by whole cells of M. tuberculosis H37Rv by 6 h of exposure. After 48 h, the inhibition was 87%, 97% and 74%, respectively. However, when the drug was added to cells taking up and metabolizing the labelled precursors at a later point (3 h for [14C]acetate and [3H]thymidine and 12 h for [14C]glycine) it inhibited completely the uptake of all the precursors, at least up to 24 h. The onset of inhibitory action was very rapid, i.e. 3 h. It is suggested that trifluoperazine has multiple sites of action and acts probably by affecting the synthesis of lipids, proteins and DNA.

Analysis of a myosin-like protein and the role of calcium in the E. coli cell cycle

For a number of years now, we have argued that current models for the control of initiation of DNA synthesis, chromosomal partitioning and septum formation in Escherichia coli are unsatisfactory. Indeed, we could argue that despite considerable efforts, with the possible exception of dnaA and ftsZ, no genes specifically implicated in these control processes have been identified. In the cases of DnaA and FtsZ, no evidence has appeared to indicate how such molecules might be regulated to act once per cycle. In 1988, we formulated a specific proposal that the timing of cell cycle events in E. coli might be determined by a Ca++ flux, mediated by calcium-binding proteins and protein kinases and culminating, in the case of chromosome segregation and division, in the action of force-generating proteins such as myosin (Norris et al., 1988). In formulating this proposal, we took the view that the fundamental elements of cell cycle regulation are likely to be highly conserved across all species including prokaryotes. In this presentation, we shall describe the approaches we have been taking in order to test this hypothesis and to summarize the data obtained, in particular in relation to new genes identified which may play a role in the E. coli cell cycle. We shall also briefly indicate recent data from other laboratories consistent with our general hypothesis.

Protein kinase activities in cell-free extracts of Streptomyces coelicolor A3(2)

Protein kinase activities were detected in cell-free extracts of the B385 derivative of Streptomyces coelicolor A3(2); at least 12 polypeptides, ranging in Mr from 6,000 to 98,000, were detectably phosphorylated, probably as O-monoesters, after incubation with gamma [32P]ATP. The culture stage of the mycelia used for production of the cell-free extracts determined the profile of phosphorylated polypeptides. Phosphoenol pyruvate acted as a potent modulator of the apparent degree of protein kinase activity. In addition Ca2+ ions, verapamil, chlorpromazine and anti-calmodulin antiserum had specific effects on the profile of phosphopolypeptides observed.