Chacon, K. | Search bioRxiv

bioRxiv2022

Intestinal Mucin Is a Chaperone of Multivalent Copper

Mucus protects the body by many mechanisms, but a role in managing toxic transition metals was not previously known. Here we report that secreted mucins, the major mucus glycoproteins coating the respiratory and intestinal epithelia, are specific copper-binding proteins. Most remarkably, the intestinal mucin, MUC2, has two juxtaposed copper binding sites, one that accommodates Cu2+ and the other Cu1+, which can be formed in situ by reduction with vitamin C. Copper is an essential trace metal because it is a cofactor for a variety of enzymes catalyzing electron transfer reactions, but copper damages macromolecules when unregulated. We observed that MUC2 protects against copper toxicity while permitting nutritional uptake into cells. These findings introduce mucins, produced in massive quantities to guard extensive mucosal surfaces, as extracellular copper chaperones and potentially important players in physiological copper homeostasis.

biochemistry↗

bioRxiv2020

Binding affinity and conformational preferences influence kinetic stability of short oligonucleotides on carbon nanotubes

DNA-wrapped single walled carbon nanotubes (SWNTs) have found a widespread use in a variety of nanotechnology applications. Yet, the relationship between structural conformation, binding affinity and kinetic stability of these polymers on SWNTs remains poorly understood. Here, we used molecular dynamics (MD) simulations and experiments to explore this relationship for short oligonucleotides adsorbed on SWNTs. First, using classical MD simulations of oligonucleotide-(9,4)-SWNT hybrid complexes, we explored the relationship between ssDNA and ssRNA surface conformation and sequence chemistry. We screened the conformation of 36 sequences of short ssDNA and ssRNA polymers on (9,4) SWNT, where the contour lengths were selected so the polymers can, to a first approximation, wrap once around the SWNT circumference. From these screens, we identified structural motifs that we broadly classified into "rings" and "non-rings." Then, several sequences were selected for detailed investigations. We used temperature replica exchange MD calculations to compute two-dimensional free energy landscapes characterizing the conformations of select sequences. "Ring" conformations seemed to be driven primarily by sequence chemistry. Specifically, strong (n,n+2) nucleotide interactions and the ability of the polymer to form compact structures, as for example, through sharp bends in the nucleotide backbone, correlated with ring-forming propensity. However, ring-formation probability was found to be uncorrelated with free energy of oligonucleotide binding to SWNTs ({Delta}Gbind). Conformational analyses of oligonucleotides, computed free energy of binding of oligonucleotides to SWNTs, and experimentally determined kinetic stability measurements show that {Delta}Gbind is the primary correlate for kinetic stability. The probability of the sequence to adopt a compact, ring-like conformation is shown to play a secondary role that still contributes measurably to kinetic stability. For example, sequences that form stable compact rings (C-rich sequences) could compensate for their relatively lower {Delta}Gbind and exhibit kinetic stability, while sequences with strong {Delta}Gbind (such as (TG)3(GT)3) were found to be kinetically stable despite their low ring formation propensity. We conclude that the stability of adsorbed oligonucleotides is primarily driven by its free energy of binding and that if ring-like structural motifs form, they would contribute positively to stability. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC="FIGDIR/small/939918v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@6483e6org.highwire.dtl.DTLVardef@10f9e60org.highwire.dtl.DTLVardef@66c8c3org.highwire.dtl.DTLVardef@68ff4_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗