Peptides, mutated

Of the various MutA leader peptide mutations generated in vivo, only Leu—7Lys and He—4Asp fully disrupted mutacin II biosynthesis, but it could not be determined what step(s) in the overall maturation process had been perturbed. Recent in vitro studies with mutants of LctA at Leu—7 showed that incorporation of any charged residue strongly perturbed lacticin 481 synthetase activity whereas the Leu—7Ala mutant was still... 

One should note in the first equation that a, , and axQ diffusion-limited rate constants, usually assumed to be independent of i, j, and k, bijk are the ligation rate constants, djk are the dissociation constants of the intermediate dimers T T , and ijk and fijk are the dissociation constants of E,NT Ti and Itljlk, respectively. The gi parameters in the second equation represent the rate constants of the background template-free ligation reactions. It is emphasized that this mechanism can be easily correlated with experimental observations because most of its parameters can be influenced by changing the environmental conditions and/or the peptide sequences. For example, the stability of the dimers and trimers under study can be finely tuned based on peptide mutations as explained above, and the rates of ligations can be controlled by changing the medium pH. 

G. Das, M. Chirumamilla, A. Toma, A. Gopalakrishnan, R.P. Zaccaria, A. Alabastri, M. Leoncini, E. Di Fabrizio, Plasmon based biosensor for distinguishing different peptides mutation states. Sci. Rep. 3, 1792 (2013)... 

By changing Ser 221 in subtilisin to Ala the reaction rate (both kcat and kcat/Km) is reduced by a factor of about 10 compared with the wild-type enzyme. The Km value and, by inference, the initial binding of substrate are essentially unchanged. This mutation prevents formation of the covalent bond with the substrate and therefore abolishes the reaction mechanism outlined in Figure 11.5. When the Ser 221 to Ala mutant is further mutated by changes of His 64 to Ala or Asp 32 to Ala or both, as expected there is no effect on the catalytic reaction rate, since the reaction mechanism that involves the catalytic triad is no longer in operation. However, the enzyme still has an appreciable catalytic effect peptide hydrolysis is still about 10 -10 times the nonenzymatic rate. Whatever the reaction mechanism... 

Figure 14.2 Models of a collagen-like peptide with a mutation Gly to Ala in the middle of the peptide (orange). Each polypeptide chain is folded into a polyproline type II helix and three chains form a superhelix similar to part of the collagen molecule. The alanine side chain is accommodated inside the superhelix causing a slight change in the twist of the individual chains, (a) Space-filling model, (b) Ribbon diagram. Compare with Figure 14.1c for the change caused by the alanine substitution. (Adapted from J. Bella et al.. Science 266 75-81, 1994.)...

Myal Y., Blanchard A., Watson P., CoRRiN M., Shiu R., Iwasiow B. Detection of genetic point mutations by peptide nucleic acid-mediated polymerase chain reaction clamping using paraffin-embedded specimens. Anal. Biochem. 2000 285 169-172. 

Sotlar K, Escribano L, Landt O, et al One-step detection of c-kit point mutations using peptide nucleic acid-mediated polymerase chain reaction clamping and hybridization probes. Am J Pathol 2003 162 737-746. 

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