Mapping and molecular modeling of S-adenosyl-L-methionine binding sites in N-methyltransferase domains of the multifunctional polypeptide cyclosporin synthetase

We employed a highly specific photoaffinity labeling procedure, using 14C-labeled S-adenosyl-L-methionine (AdoMet) to define the chemical structure of the AdoMet binding centers on cyclosporin synthetase (CySyn). Tryptic digestion of CySyn photolabeled with either [methyl-14C]AdoMet or [carboxyl-14C]AdoMet yielded the sequence H2N-Asn-Asp-Gly-Leu-Glu-Ser-Tyr-Val-Gly-Ile-Glu-Pro-Ser-Arg-COOH (residues 10644-10657), situated within the N-methyltransferase domain of module 8 of CySyn. Radiosequencing detected Glu10654 and Pro10655 as the major sites of derivatization. [carboxyl-14C]AdoMet in addition labeled Tyr10650. Chymotryptic digestion generated the radiolabeled peptide H2N-Ile-Gly-Leu-Glu-Pro-Ser-Gln-Ser-Ala-Val-Gln-Phe-COOH, corresponding to amino acids 2125-2136 of the N-methyltransferase domain of module 2. The radiolabeled amino acids were identified as Glu2128 and Pro2129, which are equivalent in position and function to the modified residues identified with tryptic digestions in module 8. Homology modeling of the N-methyltransferase domains indicates that these regions conserve the consensus topology of the AdoMet binding fold and consensus cofactor interactions seen in structurally characterized AdoMet-dependent methyltransferases. The modified sequence regions correspond to the motif II consensus sequence element, which is involved in directly complexing the adenine and ribose components of AdoMet. We conclude that the AdoMet binding to nonribosomal peptide synthetase N-methyltransferase domains obeys the consensus cofactor interactions seen among most structurally characterized low molecular weight AdoMet-dependent methyltransferases.

Analytical modeling of partially shaded photovoltaic systems

As of today, the considerable influence of select environmental variables, especially irradiance intensity, must still be accounted for whenever discussing the performance of a solar system. Therefore, an extensive, dependable modeling method is required in investigating the most suitable Maximum Power Point Tracking (MPPT) method under different conditions. Following these requirements, MATLAB-programmed modeling and simulation of photovoltaic systems is presented here, by focusing on the effects of partial shading on the output of the photovoltaic (PV) systems. End results prove the reliability of the proposed model in replicating the aforementioned output characteristics in the prescribed setting. The proposed model is chosen because it can, conveniently, simulate the behavior of different ranges of PV systems from a single PV module through the multidimensional PV structure.

Step by step analyzing, modeling and simulation of single and double array PV system in different environmental variability

This research analyses the mathematical model of the PV array with all the parameters involved, in the sequential steps. Then it is going to simulate the I-V and P-V characteristics of PV array in different climatology conditions, by using both MATLAB M-file and Simulink. Finally the capability of this method is demonstrated in simulated results, which are performed for both Single and Double Array PV system.