Biology subjects

Corless, E. I.

Publications and source records attributed to Corless, E. I..

4 recordsLinked to original sources

bioRxiv2020

Substrate sensing institutes sequential and asymmetric electron transfer in the nitrogenase-like DPOR Complex

Dark-operative protochlorophyllide oxidoreductase (DPOR) catalyzes the reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), a key penultimate step in the biosynthesis of bacteriochlorophyll. DPOR shares structural homology with nitrogenase and is made of electron donor (BchL) and electron acceptor (BchNB) component proteins. ATP driven assembly of the BchL and BchNB proteins drives electron transfer and Pchlide reduction. BchNB is composed of two subunits each of BchN and BchB arranged as an 2{beta}2 heterotetramer. Here, we describe extensive allosteric communication between the two identical active sites in BchNB that drives sequential and asymmetric electron transfer. Pchlide binding and electron transfer activities in one half of the BchNB tetramer allosterically regulates activities in the other half. Pchlide binding is sensed and recognized in trans by an Asp274 from the opposing half and is positioned in the active site to likely serve as the initial proton donor. An Asp274 to Ala substituted DPOR binds to two Pchlide molecules in the BchNB complex but is unable to conformationally poise one Pchlide molecule. Thus, stalling Pchlide reduction in both active sites. The [4Fe-4S] cluster of the BchNB protein is pre-reduced and donates the first electron to Pchlide, a mechanism similar to the deficit-spending model observed in nitrogenase. In half-reactive DPOR complexes, incapacitating proton donation in one half generates a stalled intermediate and Pchlide reduction in both halves is abolished. The results showcase long-range allosteric communication and sequential ET in the two symmetric halves. The findings shed light on the functional advantages imparted by the oligomeric architecture found in many electron transfer enzymes.

biochemistry↗

bioRxiv2019

The flexible N-terminus of BchL protects its cluster in oxygenic environments and autoinhibits activity

The dark-operative protochlorophyllide oxidoreductase (DPOR) enzyme contains two [4Fe-4S]- containing component proteins (BchL and BchNB) that assemble in an ATP-dependent fashion to coordinate electron transfer and reduction of protochlorophyllide to chlorophyllide. Photosynthesis generates an oxygenic environment that is non-optimal for [Fe-S] clusters and we here present an elegant evolutionarily conserved mechanism in BchL to protect its [4Fe-4S] cluster. We present a crystal structure of BchL in the nucleotide-free form with an ordered N-terminus that shields the [4Fe-4S] cluster at the docking interface between BchL and BchNB. Amino acid substitutions that perturb the shielding of the [4Fe-4S] cluster produce an unstable, but hyper-active enzyme complex, suggesting a role for the N-terminus in both auto-inhibition and enzyme stability. Upon ATP binding, a patch of amino acids, Asp-Phe-Asp ( DFD patch), situated at the mouth of the BchL ATP-binding pocket promotes inter-subunit cross stabilization of the two subunits and relieves the auto-inhibition by the N-terminus. A linked BchL dimer with one defective ATP-binding site does not support substrate reduction, illustrating that nucleotide binding to both subunits is a prerequisite for the inter-subunit cross stabilization. We propose that ATP-binding produces a conformational compaction of the BchL homodimer leading to a release of the flexible N-terminus from blocking the [4Fe-4S] cluster and promotes complex formation with BchNB to drive electron transfer. The auto-inhibitive feature and release mechanism appear unique to DPOR and is not found in the structurally similar nitrogenase.

biochemistry↗

bioRxiv2019

Elevated Expression of a Functional Suf Pathway in the E. coli BL21(DE3) Cell Line Enhances Recombinant Production of an Iron-Sulfur Cluster Containing Protein.

Structural and spectroscopic analysis of iron-sulfur [Fe-S] cluster-containing proteins is often limited by the occupancy and yield of recombinantly produced proteins. Here we report that Escherichia coli BL21(DE3), a strain routinely used to overexpress [Fe-S] cluster-containing proteins, has a nonfunctional Suf pathway, one of two E. coli [Fe-S] cluster biogenesis pathways. We confirmed that BL21(DE3) and commercially available derivatives carry a deletion that results in an inframe fusion of sufA and sufB genes within the sufABCDSE operon. We show that this fusion protein accumulates in cells but is - inactive in [Fe-S] biogenesis. Restoration of an intact Suf pathway combined with enhanced suf operon expression led to a remarkable (~3-fold) increase in the production of the [4Fe-4S] cluster-containing BchL protein, a key component of the dark-operative protochlorophyllide oxido-reductase complex. These results show that this engineered SufFeScient derivative of BL21(DE3) is suitable for enhanced large-scale synthesis of an [Fe-S] cluster-containing protein.\n\nIMPORTANCELarge quantities of recombinantly overexpressed iron-sulfur cluster-containing proteins are necessary for their in-depth biochemical characterization. Commercially available E. coli strain BL21(DE3) and its derivatives have a mutation that inactivates the function of one of the two native pathways (Suf pathway) responsible for cluster biogenesis. Correction of the mutation, combined with sequence changes that increase Suf expression can increase yield and cluster occupancy of [Fe-S] cluster-containing enzymes, facilitating the biochemical analysis of this fascinating group of proteins.

biochemistry↗

bioRxiv2018

Dynamics and Selective Remodeling of the DNA Binding Domains of RPA

Replication protein A (RPA) coordinates important DNA metabolic events by stabilizing single-strand DNA (ssDNA) intermediates, activating the DNA damage response, and handing off ssDNA to appropriate downstream players. Six DNA binding domains (DBDs) in RPA promote high affinity binding to ssDNA, but also allow RPA displacement by lower affinity proteins. We have made fluorescent versions of RPA and visualized the conformational dynamics of individual DBDs in the context of the full-length protein. We show that both DBD-A and DBD-D rapidly bind to and dissociate from ssDNA, while RPA as a whole remains bound to ssDNA. The recombination mediator protein Rad52 selectively modulates the dynamics of DBD-D. This demonstrates how RPA interacting proteins, with lower ssDNA binding affinity, can access the occluded ssDNA and remodel individual DBDs to replace RPA.\n\nOne Sentence SummaryThe choreography of binding and rearrangement of the individual domains of RPA during homologous recombination is revealed.

biochemistry↗