Biology subjects

Naaman, R.

Publications and source records attributed to Naaman, R..

4 recordsLinked to original sources

bioRxiv2023

The Role of Electron Spin-Polarizability and Charge Dynamics in Protein Function

Primitive nucleic acids and peptides likely collaborated during the earliest stages of biochemistry. What forces drove their interactions, and how did these forces shape the properties of primitive complexes? We investigated the association of two model primordial polypeptides with DNA. Coupling the peptides to a ferromagnetic substrate results in a dependence of the association rate and the extent of DNA binding on the orientation of magnetic moment of the substrate. The DNA binding could be nearly abolished by inverting the orientation of the magnetic field, despite the two polymers having complementary net charges. Inverting the chirality of either the entire peptide or just the connecting cysteine residue inverted the effect of the magnetic moment orientation. These results are attributed to the chiral-induced spin selectivity (CISS) effect, in which molecular chirality and electron spin interact to alter the electric polarizability of the protein. The observation of CISS effects governing simple protein-DNA complexes, suggests that this phenomenon was plausibly operative and potentially significant for primitive biomolecules. A key consequence of the CISS effect is to increase the kinetic stability of primitive protein-nucleic acid complexes. Taken together, our results show how emergent phenomena due to chirality and spin enhance bio-association.

biophysics↗

bioRxiv2022

A Possible Unitary Mechanism for General Anesthesia

The oxygen reduction reaction (ORR) is of high importance, among others because of its role in cellular respiration and in the operation of fuel cells. Recently, a possible relation between respiration and general anesthesia has been found. This work aims to explore whether anesthesia related gases affect the ORR. In ORR, oxygen which is in its triplet ground state is reduced to form products that are all in the singlet state. While this process is "in principle" forbidden because of spin conservation, it is known that if the electrons transferred in the ORR are spin polarized, the reaction occurs efficiently. Here we show, in electrochemical experiments, that the efficiency of the oxygen reduction is reduced by the presence of general anesthetics in solution. We suggest that a spin-orbit coupling to the anesthetics depolarizes the spins. This causes both a reduction in reaction efficiency and a change in the reaction products. The findings may point to a possible relation between ORR efficiency and anesthetic action. TOC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=140 SRC="FIGDIR/small/518334v2_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@4a5b8aorg.highwire.dtl.DTLVardef@1bfc961org.highwire.dtl.DTLVardef@3e002corg.highwire.dtl.DTLVardef@7d74f0_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2021

Control of protein activity by photoinduced spin polarized charge reorganization

Considerable electric fields are present within living cells, and the role of bioelectricity has been well established at the organismal level. Yet little is known about electric-field effects on protein function. Here we use phototriggered charge injection from a site-specifically attached ruthenium photosensitizer to directly demonstrate the effects of charge redistribution within a protein. We find that binding of an antibody to phosphoglycerate kinase (PGK) is increased two folds under illumination. Remarkably, illumination is found to suppress the enzymatic activity of PGK by a factor as large as three. These responses are sensitive to the photosensitizer position on the protein. Surprisingly, left (but not right) circularly polarized light elicits these responses, indicating that the electrons involved in the observed dynamics are spin polarized, due to spin filtration by protein chiral structures. Our results directly establish the contribution of electrical polarization as an allosteric signal within proteins. Future experiments with phototriggered charge injection will allow delineation of charge rearrangement pathways within proteins and will further depict their effects on protein function. Significance StatementThe role of well-placed charges within proteins in mediating biological functions, from protein-protein association to enzyme kinetics, is well documented. Here we go beyond this static picture and show that charge motions can exert significant effects on protein function. Injecting charge from a photosensitizer, we demonstrate a three-fold decrease in enzymatic activity and a two-fold increase of antibody-antigen binding. These effects depend on the specific position of the photosensitizer on the protein. Our results point to charge reorganization as a form of allostery that complements known allosteric mechanisms such as conformational changes and dynamics.

biophysics↗

bioRxiv2021

Substrates modulate charge-reorganization allosteric effects in protein-protein association

Protein function may be modulated by an event occurring far away from the functional site, a phenomenon termed allostery. While classically allostery involves conformational changes, we recently observed that charge redistribution within an antibody can also lead to an allosteric effect, modulating the kinetics of binding to target antigen. In the present study, we study the association of a poly-histidine tagged enzyme (phosphoglycerate kinase, PGK) to surface-immobilized anti-His antibodies, finding a significant Charge-Reorganization Allostery (CRA) effect. We further observe that PGKs negatively charged nucleotide substrates modulate CRA substantially, even though they bind far away from the His-tag-antibody interaction interface. In particular, binding of ATP reduces CRA by more than 50%. The results indicate that CRA may be affected by charged substrates bound to a protein and provide further insight into the role of charge redistribution in protein function. TOC GRAPHIC O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

biophysics↗