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Trinity College Dublin

Effects of heme distortion in the cytochrome subunit from Blastochloris viridis

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Lead PI: 
Prof. Mathias Senge
The effects of protein induced conformational distortion of porphyrinoid cofactors have long been believed to be a modulator of their numerous biological functions. However, explicit descriptions of the precise functional roles of particular conformations in specific proteins, beyond their citation as important, are available for only a minority subset of tetrapyrrole proteins (e.g. ferrochelatease). With this in mind, systematic investigation of the structure, effects and biological consequences of these nonplanar distortions in different biological systems is warranted. To follow from our previous work on photosynthetic reaction centers, we are investigating the possible role of conformational modulation in the control of electron transfer in the cytochrome subunit of the reaction center from Blastochloris viridis. This problem requires delineation of the various structural features that contribute to the large range of redox potentials exhibited by the chemically identical cofactors in this tetraheme cytochrome (-60 to 370mv) since other binding-site interactions (dielectric, H-bonding and steric) and substituent effects (e.g. propionate orientation and protonation state) are known to greatly influence the potentials. For our own investigations, we are primarily interested in whether the physicochemical contributions of the intrinsic structural influences (e.g. cofactor conformation) are significantly affected by the macrocycle\'s nonplanarity. This can be achieved by calculating their relative reduction potentials via high-level single-point calculations on the various conformations of each cofactor from the cytochrome subunit (taken from published crystal structures) in an isolated state. In aid of this, incremental addition of the normal-mode distortions that make-up the observed cofactor conformations to planar models of haem will show the effect and importance of each component of the conformation as well as their combined effect.\n
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