Search

Background: Research on harvesting solar energy through an artificial photosynthetic device is gaining momentum in the present era. The device is a promising solution to the energy crisis by overcoming the crunch in fossil fuel and low efficiency of heat engine. Reports are available on design of isolated parts of the photosynthetic device, for example, only sensitizer or only redox unit containing metallo-peptides. Objective: An attempt has been made to design an in silico photoreaction center in a single chain protein matrix containing all the three basic units: sensitizer, electron donor, and acceptor mimicking the photosynthetic reaction center II. Methods: A single chain of a protein containing a closely packed transmembrane four-helix bundle (PDB ID 2bl2 A) is selected for the purpose. The protein is suitably mutated in silico to accommodate the basic elements of a reaction center: Mn-Ca binding site as water oxidizing moiety, Fe-binding site as quinine reducing moiety, and MgDPP as photosensitizer to achieve the desired function of photoredox reaction. Results: A photoelectron transport protein has been designed, which may incorporate into the bilayer membrane system. It has the potential to photo-oxidize water to oxygen on one side and reduce quinone on the other side of the membrane. The stability and transmembrane orientation of the molecular device in an artificial membrane system has been validated theoretically by molecular dynamics study. Conclusion: An attempt to incorporate in silico all the elements essential for a photoelectron transport device into a single chain transmembrane protein model is the first of its kind. Donor and acceptor moieties are separated on the inner and outer side of a membrane bilayer. These features make the model unique and novel. The design of the model is the first step towards the study of experimental viability of the model, which remains to be validated in future.

A method has been developed to calculate and represent the geometry of α-helices of membrane proteins. Geometrical parameters are computed from coordinate files in the protein data bank. The axis of the helix is determined from the local centroids of tetrapeptide units of the helix. The method provides lower and upper cutoff values of the distance between backbone atoms C i(carbonyl carbon) and N i+4 for allocation of a hinge in a helix. The method calculates other geometrical parameters like the length of helix, twist per residue, height per residue, kink and swivel angles. Packing of bundles of α-helices is represented by relative angles of inclination and distance vectors. The parameters are useful in quantitative descriptions of structural features of membrane proteins. Figure Representation of the organization of the helix bundle in 1rwt by helix axis Θ 1( i)- Θ n( i), helix center Θ 0( i) of i th helix and centroid (C) of centers the three helices. Arrow-head indicates C-terminal end of a helix.

On the basis of existing evidence, a model is proposed for the topology of carotenoids in photosystem II (PS II) of chloroplasts, suggesting their possible roles in the photoprotection and stability of PS II complex. The presence of one cis and one trans β-carotene at reaction centre II (RC II), with different photoprotective functions, is suggested. The core antennae (CP43, CP47) are presumed to contain β-carotene molecules in clusters. The possible molecular mechanism for formation of a quenching complex in the minor LHC II, involving zeaxanthin, chlorophyll a and the glutamic acid side chain of the light harvesting protein, is worked out. This complex is proposed to be an efficient triplet quencher, in addition to its role as a quencher of singlet chlorophyll energy. The migration of triplet energy from RC II to the quenching complex is surmised. It is suggested that the carotenoids in RC II and in different LHCs form an integrated photoprotective unit.

On the basis of existing evidence, a model is proposed for the topology of carotenoids in photosystem II (PS II) of chloroplasts, suggesting their possible roles in the photoprotection and stability of PS II complex. The presence of one cisand one transß-carotene at reaction centre II (RC II), with different photoprotective functions, is suggested. The core antennae (CP43, CP47) are presumed to contain ß-carotene molecules in clusters. The possible molecular mechanism for formation of a quenching complex in the minor LHC II, involving zeaxanthin, chlorophyll aand the glutamic acid side chain of the light harvesting protein, is worked out. This complex is proposed to be an efficient triplet quencher, in addition to its role as a quencher of singlet chlorophyll energy. The migration of triplet energy from RC II to the quenching complex is surmised. It is suggested that the carotenoids in RC II and in different LHCs form an integrated photoprotective unit.