Cotranslational protein assembly imposes evolutionary constraints on homomeric proteins

Cotranslational protein folding can facilitate rapid formation of functional structures. However, it might also cause premature assembly of protein complexes, if two interacting nascent chains are in close proximity. By analyzing known protein structures, we show that homomeric protein contacts are enriched towards the C-termini of polypeptide chains across diverse proteomes. We hypothesize that this is the result of evolutionary constraints for folding to occur prior to assembly. Using high-throughput imaging of protein homomers in vivo in E. coli and engineered protein constructs with N- and C-terminal oligomerization domains, we show that, indeed, proteins with C-terminal homomeric interface residues consistently assemble more efficiently than those with N-terminal interface residues. Using in vivo, in vitro and in silico experiments, we identify features that govern successful assembly of homomers, which have implications for protein design and expression optimization

Furfural-Derived Diacid Prepared by Photoreaction for Sustainable Materials Synthesis

A <i>cis</i>-3,4-di­(furan-2-yl)­cyclobutane-1,2-dicarboxylic acid (<b>CBDA-2</b>) is readily prepared stereospecifically from <i>trans</i>-3-(2-furyl)­acrylic acid, a furfural-derived compound, through a solid-state [2 + 2] photocycloaddition in 95% isolated yield. The cyclobutane ring in <b>CBDA-2</b> shows desired stabilities during thermal, sunlight, and chemical tests. The single crystal structure of <b>CBDA-2</b> revealed the geometry of this molecule and orientation of the two dicarboxylic acid groups displaying its potential to serve as a unique, semirigid diacid building block in material science. A preliminary study showed that condensation of this diacid with glycerol yielded a green polymer with good stability. The diacid could also be used as a cross-linker for a biobased epoxy to yield an exceptionally hard and solvent-resistant thermoset

A Naphtho‑<i>p</i>‑quinodimethane Exhibiting Baird’s (Anti)Aromaticity, Broken Symmetry, and Attractive Photoluminescence

We report a novel reductive desulfurization reaction involving π-acidic naphthalene diimides (NDI) <b>1</b> using thionating agents such as Lawesson’s reagent. Along with the expected thionated NDI derivatives <b>2</b>–<b>6</b>, new heterocyclic naphtho-<i>p</i>-quinodimethane compounds <b>7</b> depicting broken/reduced symmetry were successfully isolated and fully characterized. Empirical studies and theoretical modeling suggest that <b>7</b> was formed via a six-membered ring oxathiaphosphenine intermediate rather than the usual four-membered ring oxathiaphosphetane of <b>2</b>–<b>6</b>. Aside from the reduced symmetry in <b>7</b> as confirmed by single-crystal XRD analysis, we established that the ground state UV–vis absorption of <b>7</b> is red-shifted in comparison to the parent NDI <b>1</b>. This result was expected in the case of thionated polycyclic diimides. However, unusual low energy transitions originate from Baird 4nπ aromaticity of compounds <b>7</b> in lieu of the intrinsic Hückel (4n + 2)­π aromaticity as encountered in NDI <b>1</b>. Moreover, complementary theoretical modeling results also corroborate this change in aromaticity of <b>7</b>. Consequently, photophysical investigations show that, compared to parent NDI <b>1</b>, <b>7</b> can easily access and emit from its T₁ state with a phosphorescence ³(<b>7a</b>)* lifetime of τ_P = 395 μs at 77 K indicative of the formation of the corresponding “aromatic triplet” species according to the Baird’s rule of aromaticity