Distinction of sperm-binding site and reactive site for trypsin inhibition on p12 secreted from the accessory sex glands of male mice

Six variants of P12, a Kazal-type trypsin inhibitor in the secretion of male mouse accessory sexual glands, were made using single-site mutations including R19L, Y21V, D22G, R43G, K44S, and R45T, based on one-letter-code mutation of amino acids. The other two variants, Nd10 and Cd8, were made using the deletion of 10 and 8 residues from the N- and C-terminals, respectively. Their CD profiles revealed maintenance of the P12 conformation in the seven variants, excluding Cd8, which became unfolded. Only R19L entirely lost the ability while the other variants were as strong as P12 in inhibiting the trypsin digestion of N-benzoyl-Phe-Val-Arg 7-amido-4-methylcoumarin. The immunocytochemical results demonstrated that D22G and Cd8 failed to bind to sperm, Y21V very weakly did so, and the other variants retained their sperm-binding abilities. Concomitantly, the immunocytochemical stainability of each ligand was parallel to its inhibitory effect on 125I-P12-sperm binding, and a synthetic oligopeptide corresponding to residues 18-24 of P12 was able to inhibit P12-sperm binding. The data together concluded that R19 was essential for protease inhibition and D22 and/or Y21 mainly being responsible for the binding of P12 to sperm. The steric arrangement of R19, Y21, and D22 on the tertiary structure of P12 is discussed.     

Gene cloning and molecular characterization of lysine decarboxylase from Selenomonas ruminantium delineate its evolutionary relationship to ornithine decarboxylases from eukaryotes

Lysine decarboxylase (LDC; EC 4.1.1.18) from Selenomonas ruminantium comprises two identical monomeric subunits of 43 kDa and has decarboxylating activities toward both L-lysine and L-ornithine with similar K(m) and V(max) values (Y. Takatsuka, M. Onoda, T. Sugiyama, K. Muramoto, T. Tomita, and Y. Kamio, Biosci. Biotechnol. Biochem. 62:1063-1069, 1999). Here, the LDC-encoding gene (ldc) of this bacterium was cloned and characterized. DNA sequencing analysis revealed that the amino acid sequence of S. ruminantium LDC is 35% identical to those of eukaryotic ornithine decarboxylases (ODCs; EC 4.1.1.17), including the mouse, Saccharomyces cerevisiae, Neurospora crassa, Trypanosoma brucei, and Caenorhabditis elegans enzymes. In addition, 26 amino acid residues, K69, D88, E94, D134, R154, K169, H197, D233, G235, G236, G237, F238, E274, G276, R277, Y278, K294, Y323, Y331, D332, C360, D361, D364, G387, Y389, and F397 (mouse ODC numbering), all of which are implicated in the formation of the pyridoxal phosphate-binding domain and the substrate-binding domain and in dimer stabilization with the eukaryotic ODCs, were also conserved in S. ruminantium LDC. Computer analysis of the putative secondary structure of S. ruminantium LDC showed that it is approximately 70% identical to that of mouse ODC. We identified five amino acid residues, A44, G45, V46, P54, and S322, within the LDC catalytic domain that confer decarboxylase activities toward both L-lysine and L-ornithine with a substrate specificity ratio of 0.83 (defined as the k(cat)/K(m) ratio obtained with L-ornithine relative to that obtained with L-lysine). We have succeeded in converting S. ruminantium LDC to form with a substrate specificity ratio of 58 (70 times that of wild-type LDC) by constructing a mutant protein, A44V/G45T/V46P/P54D/S322A. In this study, we also showed that G350 is a crucial residue for stabilization of the dimer in S. ruminantium LDC.     

The complete amino acid sequence of coagulogen isolated from Southeast Asian horseshoe crab, Carcinoscorpius rotundicauda

The complete amino acid sequence of coagulogen purified from the hemocytes of the horseshoe crab Carcinoscorpius rotundicauda was determined by characterization of the NH2-terminal sequence and the peptides generated after digestion of the protein with lysyl endopeptidase, Staphylococcal aureus protease V8 and trypsin. Upon sequencing the peptides by the automated Edman method, the following sequence was obtained: A D T N A P L C L C D E P G I L G R N Q L V T P E V K E K I E K A V E A V A E E S G V S G R G F S L F S H H P V F R E C G K Y E C R T V R P E H T R C Y N F P P F V H F T S E C P V S T R D C E P V F G Y T V A G E F R V I V Q A P R A G F R Q C V W Q H K C R Y G S N N C G F S G R C T Q Q R S V V R L V T Y N L E K D G F L C E S F R T C C G C P C R N Y Carcinoscorpius coagulogen consists of a single polypeptide chain with a total of 175 amino acid residues and a calculated molecular weight of 19,675. The secondary structure calculated by the method of Chou and Fasman reveals the presence of an alpha-helix region in the peptide C segment (residue Nos. 19 to 46), which is released during the proteolytic conversion of coagulogen to coagulin gel. The beta-sheet structure and the 16 half-cystines found in the molecule appear to yield a compact protein stable to acid and heat. The amino acid sequences of coagulogen of four species of limulus have been compared and the interspecies evolutionary differences are discussed.     

Regions of the amino terminus of the P2X1 receptor required for modification by phorbol ester and mGluR1α receptors

The potentiation of P2X₁ receptor currents by phorbol ester (PMA) treatment and stimulation of mGluR1α receptors was sensitive to inhibition of novel forms of protein kinase C. Potentiation was also reduced by co-expression of an amino terminal P2X₁ receptor minigene. Cysteine point mutants of residues Tyr¹⁶-Gly³⁰ were expressed in Xenopus oocytes. Peak current amplitudes to ATP for Y16C, T18C and R20C mutants were reduced, however this did not result from a decrease in surface expression of the channels. The majority of the mutants showed changes in the time-course of desensitization of ATP evoked currents indicating the important role of this region in regulation of channel properties. PMA and mGluR1α potentiation was abolished for the mutants Y16C, T18C, R20C, K27C and G30C. Minigenes incorporating either Y16C, K27C, V29C or G30C still inhibited PMA responses. However D17C, T18C or R20C mutant minigenes were no longer effective suggesting that these residues are important for interaction with regulatory factors. These results demonstrate that the conserved YXTXK/R sequence and a region with a conserved glycine residue close to the first transmembrane segment contribute to PMA and GPCR regulation of P2X₁ receptors.     

Increased alkali stability in Trichoderma reesei endo-1, 4-beta-xylanase II by site directed mutagenesis

A number of engineered Trichoderma reesei endo-beta-1,4-xylanase (Xyn II) mutants were created and activity tests were performed for increased stability. The stability of the earlier characterized mutant Y5 (T2C, T28C, K58R, +191D) was further increased by the mutations creating the constructs P9 (N97R+F93W+H144K), P12 (H144C+N92C), P15 (F180Q+H144C+N92C) and P21 (H22K+F180Q+H144C+N92C). The resistance towards thermal inactivation at alkaline pH was increased in all of the mutants. Residual activity T(50%) was increased 4-5 degrees C for P9 at pH 9. The performance of the P9 mutant in sulphate pulp bleaching was also tested and was shown to increase brightness markedly compared to the reference. The bleaching results showed the industrial potential of the obtained mutant.     

A peptide from the eel pancreas with structural similarity to human pancreatic secretory trypsin inhibitor

The primary structure of a 61-amino-acid residue peptide from the pancreas of the European eel (Anguilla anguilla) has been established as E E K S G(5)L Y R K P(10)S C G E M(15)S A M H A(20)C P M N F(25)A P V C G(30)T D G N T(35)Y P N E C(40)S L C F Q(45)R Q N T K(50)T D I L I(55)T K D D R(60)C. There was no indication of microheterogeneity. This peptide shows structural similarity to pancreatic secretory trypsin inhibitors from several mammalian species and to a cholecystokinin-releasing peptide isolated from rat pancreatic juice. A comparison of the amino acid sequences of the peptides has identified a domain in the central region of the molecules that has been strongly conserved during evolution. In contrast, the amino acid sequence in the region corresponding to the reactive centre of the mammalian trypsin inhibitors is very poorly conserved in the eel peptide. The P1-P1' reactive site lysine-isoleucine (or arginine-isoleucine) bond in the mammalian trypsin inhibitors is replaced by a methionine-asparagine bond. This region does, however, show limited homology to the reactive centre of human alpha 1-protease inhibitor suggesting that the eel peptide may function as an inhibitor of other proteolytic enzymes in the pancreas.     

Isolation and Characterization of Pediocin AcH Chimeric Protein Mutants with Altered Bactericidal Activity

A collection of pediocin AcH amino acid substitution mutants was generated by PCR random mutagenesis of DNA encoding the bacteriocin. Mutants were isolated by cloning mutagenized DNA into an Escherichia coli malE plasmid that directs the secretion of maltose binding protein-pediocin AcH chimeric proteins and by screening transformant colonies for bactericidal activity against Lactobacillus plantarum NCDO955 (K. W. Miller, R. Schamber, Y. Chen, and B. Ray, 1998. Appl. Environ. Microbiol. 64:14–20, 1998). In all, 17 substitution mutants were isolated at 14 of the 44 amino acids of pediocin AcH. Seven mutants (N5K, C9R, C14S, C14Y, G37E, G37R, and C44W) were completely inactive against the pediocin AcH-sensitive strains L. plantarum NCDO955, Listeria innocua Lin11, Enterococcus faecalis M1, Pediococcus acidilactici LB42, and Leuconostoc mesenteroides Ly. A C24S substitution mutant constructed by other means also was inactive against these bacteria. Nine other mutants (K1N, W18R, I26T, M31T, A34D, N41K, H42L, K43N, and K43E) retained from <1% to ~60% of wild-type activity when assayed against L. innocua Lin11. One mutant, K11E, displayed ~2.8-fold-higher activity against this indicator. About one half of the mutations mapped to amino acids that are conserved in the pediocin-like family of bacteriocins. All four cysteines were found to be required for activity, although only C9 and C14 are conserved among pediocin-like bacteriocins. Several basic amino acids as well as nonpolar amino acids located within the hydrophobic C-terminal region also were found to be important. The mutations are discussed in the context of structural models that have been proposed for the bacteriocin.     

Cysteine mutagenesis of the amino acid residues of transmembrane helix I in the melibiose carrier of Escherichia coli

The melibiose carrier of Escherichia coli is a sugar-cation cotransport system that utilizes Na(+), Li(+), or H(+). This membrane transport protein consists of 12 transmembrane helices. Starting with the cysteine-less melibiose carrier, cysteine has been substituted individually for amino acids 17-37, which includes all of the residues in membrane helix I. The carriers with cysteine substitutions were studied for their transport activity and the effect of the water soluble sulfhydryl reagent p-chloro- mercuribenzenesulfonic acid (PCMBS). Cysteine substitution caused loss of transport activity in six of the mutants (G17C, K18C, D19C, Y32C, T34C, and D35C). PCMBS caused greater than 50% inhibition in eleven mutants (F20C, A21C, I22C, G23C, I24C, V25C, Y26C, M27C, Y28C, M30C, and Y31C). We suggest that the residues whose cysteine derivatives were inhibited by PCMBS face the aqueous channel and that helix I is completely surrounded by aqueous environment. Second site revertants were isolated from K18C and Y31C. The revertants were found to have mutations in helices I, IV, and VII.     

非特异性脂质转移蛋白突变体的构建及在两种硫氧还蛋白表达载体中的表达比较

对水稻非特异性脂质转移蛋白(Nospecific lipid transfer protein,nsLTP) LTP110中结构重要的5个氨基酸位点进行了定点突变,测序结果证实了突变体构建成功。在尝试了多种大肠杆菌表达系统进行表达之后,发现硫氧还蛋白融合表达载体适合于LTP110野生型及突变体的表达。将编码野生型LTP110及突变体Y17A,P72L,R46A,D45A,C50A蛋白的cDNA顺序克隆进两种硫氧还蛋白表达载体并对其表达情况进行了比较：pTrxFus载体可以在宿主菌GI724中以较低水平表达野生型LTP110及突变体Y17A,P72L,R46A融合蛋白,但不能表达D45A和C50A融合蛋白;pET32a(+)载体可以在宿主菌BL21 (DE3) trxB-中以可溶蛋白的形式表达野生型及所有突变型融合蛋白,且表达量比在pTrxFus载体/GI724突主菌中表达量高。对pET32a(+)载体中表达的LTP110融合蛋白进行了纯化,并利用带有荧光标记的脂肪酸分子对其测活,结果表明表达的野生型LTP110分子具有结合脂质的活性。     

Importance of individual amino acids in the Switch I region in eEF2 studied by functional complementation in S. cerevisiae

Elongation factor 2 (eEF2) is a member of the G-protein super family. G-proteins undergo conformational changes associated with binding of the guanosine nucleotide and hydrolysis of the bound GTP. These structural rearrangements affects the Switch I region (also known as the Effector loop). We have studied the role of individual amino acids in the Switch I region (amino acids 25-73) of S. cerevisiae eEF2 using functional complementation in yeast. 21 point mutations in the Switch I region were created by site-directed mutagenesis. Mutants K49R, E52Q, A53G, F55Y, K60R, Q63A, T68S, I69M and A73G were functional while mutants R54H, F55N, D57A, D57E, D57S, R59K, R59M, Q63E, R65A, R65N, T68A and T68M were inactive. Expression of mutants K49R, A53G, Q63A, I69M and A73G was associated with markedly decreased growth rates and yeast cells expressing mutants A53G and I69M became temperature sensitive. The functional capacity of eEF2 in which the major part Switch I (amino acids T56 to I69) was converted into the homologous sequence found in EF-G from E. coli was also studied. This protein chimera could functionally replace yeast eEF2 in vivo. Yeast cells expressing this mutant grew extremely slowly, showed increased cell death and became temperature sensitive. The ability of the mutant to replace authentic eEF2 in vivo indicates that the structural rearrangement of Switch I necessary for eEF2 function is similar in eukaryotes and bacteria. The effect of two point mutations in the P-loop was also studied. Mutant A25G but not A25V could functionally replace yeast eEF2 even if cells expressing the mutant grew slowly. The A25G mutation converted the consensus sequences AXXXXGK[T/S] in eEF2 to the corresponding motif GXXXXGK[T/S] found in all other G-proteins, suggesting that the alanine found in the P-loop of peptidyltranslocases are not essential for function.     

The region from phenylalanine-17 to phenylalanine-28 of a yeast mitochondrial ATPase inhibitor is essential for its ATPase inhibitory activity.

Mitochondrial ATP synthase (F(1)F(o)-ATPase) is regulated by an intrinsic ATPase inhibitor protein. In the present study, we investigated the structure-function relationship of the yeast ATPase inhibitor by amino acid replacement. A total of 22 mutants were isolated and characterized. Five mutants (F17S, R20G, R22G, E25A, and F28S) were entirely inactive, indicating that the residues, Phe17, Arg20, Arg22, Glu25, and Phe28, are essential for the ATPase inhibitory activity of the protein. The activity of 7 mutants (A23G, R30G, R32G, Q36G, L37G, L40S, and L44G) decreased, indicating that the residues, Ala23, Arg30, Arg32, Gln36, Leu37, Leu40, and Leu44, are also involved in the activity. Three mutants, V29G, K34Q, and K41Q, retained normal activity at pH 6.5, but were less active at pH 7.2, indicating that the residues, Val29, Lys34, and Lys41, are required for the protein's action at higher pH. The effects of 6 mutants (D26A, E35V, H39N, H39R, K46Q, and K49Q) were slight or undetectable, and the residues Asp26, Glu35, His39, Lys46, and Lys49 thus appear to be dispensable. The mutant E21A retained normal ATPase inhibitory activity but lacked pH-sensitivity. Competition experiments suggested that the 5 inactivated mutants (F17S, R20G, R22G, E25A, and F28S) could still bind to the inhibitory site on F(1)F(o)-ATPase. These results show that the region from the position 17 to 28 of the yeast inhibitor is the most important for its activity and is required for the inhibition of F(1), rather than binding to the enzyme.     

Sequence-specific 1H-n.m.r. assignments and peptide backbone conformation in rat epidermal growth factor.

The solution conformation of rat epidermal growth factor (EGF) has been investigated by proton n.m.r. techniques. Two-dimensional proton n.m.r. experiments have allowed sequential resonance assignments to be made for most protons. On the basis of these assignments, two regions of anti-parallel beta-sheet structure have been derived from the n.m.r. data. A beta-sheet segment running from about V19 to V23 (capital letters refer to amino acids in the single-letter notation) is folded onto a beta-sheet segment running from R28 to N32 and joined by a chain reversal from E24 to D27. A second region involves a beta-turn from V34 to Y37, which starts a short beta-sheet up to G39, followed by a chain reversal up to Q43, which leads to folding of the C-terminal beta-sheet segment, i.e. H44-R45, running antiparallel to the short Y37 beta-sheet segment. The N-terminal segment up to G18 exists in a multiple bend conformation and is folded on to the V29-V23/R28-N32 beta-sheet such that Y10, Y13, Y22 and Y29 are proximal to each other. Structural comparison of rat, murine and human EGFs indicates a number of highly conserved structural features common to at least these species of EGF.     

Characterization of pncA mutations in pyrazinamide-resistant Mycobacterium tuberculosis isolates from Korea and analysis of the correlation between the mutations and pyrazinamidase activity

To investigate the effect of natural pyrazinamidase (PncA) mutations on protein function, we analyzed expression and PncA activity of eight pncA point mutants identified in nineteen pyrazinamide-resistant Mycobacterium tuberculosis clinical isolates. Among them, two mutants (Y99D and T135P) showed high expression level and solubility comparable to those of the wild-type PncA protein, two (K48E and G97D) displayed low expression level and solubility, and four (C14R, H51P, W68S, and A146V) were insoluble. Interestingly, when possible structural effects of these mutations were predicted by the CUPSAT program based on the proposed three-dimensional structure of M. tuberculosis PncA, only two highly soluble mutant proteins (Y99D and T135P) were predicted to be stabilizing and have favorable torsion angles. However, the others exhibiting either low solubility or precipitation were foreseen to be destabilizing and/or have unfavorable torsion angles, suggesting that the alterations could interfere with proper protein folding, thereby decreasing or depleting protein solubility. A PncA activity assay demonstrated that two mutants (G97D and T135P) showed virtually no activity, but two other mutants (K48E and Y99D) exhibited wild-type activity, indicating that the PncA residues (Cys14, His51, Trp68, Gly97, Thr135, and Ala146) may be important for PncA activity and/or proper protein folding.     

The complete amino acid sequence of the low molecular weight cytosolic acid phosphatase

This paper presents the complete amino acid sequence of the low molecular weight acid phosphatase from bovine liver. This isoenzyme of the acid phosphatase family is located in the cytosol, is not inhibited by L-(+)-tartrate and fluoride ions, but is inhibited by sulfhydryl reagents. The enzyme consists of 157 amino acid residues, has an acetylated NH2 terminus, and has arginine as the COOH-terminal residue. All 8 half-cystine residues are in the free thiol form. The molecular weight calculated from the sequence is 17,953. The sequence was determined by characterizing the peptides purified by reverse-phase high performance liquid chromatography from tryptic, thermolytic, peptic, Staphylococcus aureus protease, and chymotryptic digests of the carboxymethylated protein. No sequence homologies were found with the two known acylphosphatase isoenzymes or the metalloproteins porcine uteroferrin and purple acid phosphatase from bovine spleen (both of which have acid phosphatase activity). Two half-cystines at or near the active site were identified through the reaction of the enzyme with [14C] iodoacetate in the presence or in the absence of a competitive inhibitor (i.e. inorganic phosphate). Ac-A E Q V T K S V L F V C L G N I C R S P I A E A V F R K L V T D Q N I S D N W V I D S G A V S D W N V G R S P N P R A V S C L R N H G I N T A H K A R Q V T K E D F V T F D Y I L C M D E S N L R D L N R K S N Q V K N C R A K I E L L G S Y D P Q K Q L I I E D P Y Y G N D A D F E T V Y Q Q C V R C C R A F L E K V R-OH.     

Evolution of trypsinogen activation peptides

The activation peptide of mammalian trypsinogens contains a highly conserved tetra-aspartate sequence (D19-D20-D21-D22) preceding the K23-I24 scissile peptide bond, which is hydrolyzed as the first step in the activation process. Here, we examined the evolution and function of trypsinogen activation peptides through integrating functional characterization of disease-associated mutations with comparative genomic analysis. Activation properties of three chronic pancreatitis-associated activation peptide mutants (the novel D19A and the previously reported D22G and K23R) were simultaneously analyzed, for the first time, in the context of recombinant human cationic trypsinogen. A dramatic increase in autoactivation of cationic trypsinogen was observed in all three mutants, with D22G and K23R exhibiting the most marked increases. The physiological activator enteropeptidase activated the D19A mutant normally, activated the D22G mutant very poorly, and stimulated activation of the K23R mutant. The biochemical and structural data, taken together with a comprehensive sequence comparison, indicates that the tetra-aspartate sequence in mammalian trypsinogen activation peptides has evolved not only for optimal enteropeptidase recognition in the duodenum but also for efficient inhibition of trypsinogen autoactivation within the pancreas. Moreover, the use of lysine instead of arginine at the P1 position of activation peptides also has an advantageous effect against trypsinogen autoactivation. Finally, fixed substitutions in the key residues of the trypsinogen activation peptide may suggest the evolution of new functions unrelated to digestion, as found in the group III trypsinogens of cold-adapted fishes.     

Y55 and D78 are crucial amino acid residues of a new IgE epitope on trichosanthin

Trichosanthin (TCS) possesses many biological and pharmaceutical activities, but its strong immunogenicity limits its clinical application. To reduce the immunogenicity of TCS, we modified the reported method for the prediction of antigenic site and identified two crucial amino acid residues (Y55 and D78) for a new epitope. We mutated these two residues into glycine and serine, respectively, and obtained three mutants, Y55G, D78S, and Y55G/D78S. These mutants induced less amount of Ig and IgG antibodies in C57BL/6J mice than wild-type TCS (wTCS) (p<0.01) and almost lost the ability to induce IgE antibody production. The mutants stimulated fewer TCS-specific B cells in C57BL/6J mice than wTCS (p<0.01). Compared with wTCS, Y55G, D78S, and Y55G/D78S lost 26.9%, 17.9%, and 98.7% specific binding ability to anti-TCS monoclonal antibody TCS4E9, respectively. These mutants still retained RNA N-glycosidase activity. In conclusion, Y55 and D78 are two crucial amino acid residues of a new IgE epitope on TCS, and their mutation reduces the immunogenicity of TCS, but still retained the enzymatic activity.     

Genetic characterization of the (534)DPPR motif of the yeast plasma membrane H(+)-ATPase

The highly conserved motif +(534)DPPR of Saccharomyces cerevisiae H(+)-ATPase, located in the putative ATP binding site, has been mutagenized and the resulting 23 mutant genes conditionally expressed in secretory vesicles. Fourteen mutant ATPases (D534A, D534V, D534L, D534N, D534G, D534T, P535A, P535V, P535L, P535G, P535T, P535E, P535K and R537T) failed to reach the secretory vesicles. Of these mutants, nine (D534N, D534T, P535A, P535V, P535L, P535G, P535T, P535E and P535K) were not detected in total cellular membranes, and five (D534A, D534V, D534G, D534L and R537T) were retained at the endoplasmic reticulum and exhibited a dominant lethal phenotype. The remaining mutants (D534E, R537A, R537V, R537L, R537N, R537G, R537E, R537K and R537H) reached the secretory vesicles at levels similar to that of the wild type. Of these, six (R537A, R537V, R537L, R537N, R537G, and R537E) showed severely decreased ATPase activity compared to the wild type enzyme, and three (D534E, R537K and R537H) rendered an enzyme with an altered K(m) for ATP.     

Phosphorylation and mutation of human cardiac troponin I deferentially destabilize the interaction of the functional regions of troponin I with troponin C

We have utilized 2D [(1)H,(15)N]HSQC NMR spectroscopy to elucidate the binding of three segments of cTnI in native, phosphorylated, and mutated states to cTnC. The near N-terminal region (cRp; residues 34-71) contains the protein kinase C (PKC) phosphorylation sites S41 and S43, the inhibitory region (cIp; residues 128-147) contains another PKC site T142 and a familial hypertrophic cardiomyopathy (FHC) mutation R144G, and the switch region (cSp; residues 147-163) contains the novel p21-activated kinase (PAK) site S149 and another FHC mutation R161W. While S41/S43 phosphorylation of cRp had minimal disruption in the interaction of cRp and cTnC.3Ca(2+), T142 phosphorylation reduced the affinity of cIp for cCTnC.2Ca(2+) by approximately 14-fold and S149 phosphorylation reduced the affinity of cSp for cNTnC.Ca(2+) by approximately 10-fold. The mutation R144G caused an approximately 6-fold affinity decrease of cIp for cCTnC.2Ca(2+) and mutation R161W destabilized the interaction of cSp and cNTnC.Ca(2+) by approximately 1.4-fold. When cIp was both T142 phosphorylated and R144G mutated, its affinity for cCTnC.2Ca(2+) was reduced approximately 19-fold, and when cSp was both S149 phosphorylated and R161W mutated, its affinity for cNTnC.Ca(2+) was reduced approximately 4-fold. Thus, while the FHC mutation R144G enhances the effect of T142 phosphorylation on the interaction of cIp and cCTnC.2Ca(2+), the FHC mutation R161W suppresses the effect of S149 phosphorylation on the interaction of cSp and cNTnC.Ca(2+), demonstrating linkages between the FHC mutation and phosphorylation of cTnI. The observed alterations corroborate well with structural data. These results suggest that while the modifications in the cRp region have minimal influence, those in the key functional cIp-cSp region have a pronounced effect on the interaction of cTnI and cTnC, which may correlate with the altered myofilament function and cardiac muscle contraction under pathophysiological conditions.     

Exploring the cause of drug resistance by the detrimental missense mutations in KIT receptor: computational approach

In this work, we computationally identified the most detrimental missense mutations of KIT receptor causing gastrointestinal stromal tumors and analyzed the drug resistance of these missense mutations. Out of 31 missense mutations, 19 variants were commonly found less stable, deleterious and damaging by I-Mutant 2.0, SIFT and PolyPhen programs, respectively. Subsequently, we performed modeling of these 19 variants to understand their change in conformations with respect to native KIT receptor by computing their RMSD. Further, the native and 19 mutants were docked with the drug ‘Imatinib’ to explain the drug resistance of these detrimental missense mutations. Among the 19 mutants, we found by docking studies that 12 mutants, namely, F584C, F584L, V654A, L656P, T670I, R804W, D816F, D816V, D816Y, N822K, Y823D and E839K had less binding affinity with Imatinib than the native type. Finally, we analyzed that the loss of binding affinity of these 12 mutants, was due to altered flexibility in their binding amino acids with Imatinib as compared with native type by normal mode analysis. In our work, we found the novel data that the majority of the drug-binding amino acids in those 12 mutants had encountered loss of flexibility, which could be the theoretical basis for the cause of drug insensitivity.     

Structural studies of the N-terminus of Connexin 32 using H NMR spectroscopy

The amino terminus of gap junction proteins, connexins, plays a fundamental role in voltage gating and ion permeation. We have previously shown with ¹H NMR that the structure of the N-terminus of a representative connexin molecule contains a flexible turn around glycine 12 [P.E. Purnick, D.C. Benjamin, V.K. Verselis, T.A. Bargiello, T.L. Dowd, Arch. Biochem. Biophys. 381 (2000) 181-190] allowing the N-terminus to reside at the cytoplasmic entry of the channel forming a voltage-sensor. Previous functional studies or neuropathies have shown that the mutation G12Y and G12S form non-functional channels while functional channels are formed from G12P. Using 2D ¹H NMR we show that similar to G12, the structure of the G12P mutant contains a more flexible turn around residue 12, whereas the G12S and G12Y mutants contain tighter, helical turns in this region. These results suggest an unconstrained turn is required around residue 12 to position the N-terminus within the pore allowing the formation of the cytoplasmic channel vestibule, which appears to be critical for proper channel function.