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Precise protein sequencing and folding are believed to generate the structure and chemical diversity of natural channels(1,2), both of which are essential to synthetically achieve proton transport performance comparable to that seen in natural systems. Geometrically defined channels have been fabricated using peptides, DNAs, carbon nanotubes, sequence-defined polymers and organic frameworks(3-13). However, none of these channels rivals the performance observed in their natural counterparts. Here we show that without forming an atomically structured channel, four-monomer-based random heteropolymers (RHPs)(14) can mimic membrane proteins and exhibit selective proton transport across lipid bilayers at a rate similar to those of natural proton channels. Statistical control over the monomer distribution in an RHP leads to segmental heterogeneity in hydrophobicity, which facilitates the insertion of single RHPs into the lipid bilayers. It also results in bilayer-spanning segments containing polar monomers that promote the formation of hydrogen-bonded chains(15,16) for proton transport. Our study demonstrates the importance of the adaptability that is enabled by statistical similarity among RHP chains and of the modularity provided by the chemical diversity of monomers, to achieve uniform behaviour in heterogeneous systems. Our results also validate statistical randomness as an unexplored approach to realize protein-like behaviour at the single-polymer-chain level in a predictable manner.

The mid-Cretaceous period was one of the warmest intervals of the past 140 million years(1-5), driven by atmospheric carbon dioxide levels of around 1,000 parts per million by volume(6). In the near absence of proximal geological records from south of the Antarctic Circle, it is disputed whether polar ice could exist under such environmental conditions. Here we use a sedimentary sequence recovered from the West Antarctic shelf-the southernmost Cretaceous record reported so far-and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82 degrees S during the Turonian-Santonian age (92 to 83 million years ago). This record contains an intact 3-metre-long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores. A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1,120-1,680 parts per million by volume and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide.

Elucidating the mechanism of sugar import requires a molecular understanding of how transporters couple sugar binding and gating events. Whereas mammalian glucose transporters (GLUTs) are specialists(1), the hexose transporter from the malaria parasite Plasmodium falciparum PfHT1(2,3) has acquired the ability to transport both glucose and fructose sugars as efficiently as the dedicated glucose (GLUT3) and fructose (GLUT5) transporters. Here, to establish the molecular basis of sugar promiscuity in malaria parasites, we determined the crystal structure of PfHT1 in complex with d-glucose at a resolution of 3.6 angstrom. We found that the sugar-binding site in PfHT1 is very similar to those of the distantly related GLUT3 and GLUT5 structures(4,5). Nevertheless, engineered PfHT1 mutations made to match GLUT sugar-binding sites did not shift sugar preferences. The extracellular substrate-gating helix TM7b in PfHT1 was positioned in a fully occluded conformation, providing a unique glimpse into how sugar binding and gating are coupled. We determined that polar contacts between TM7b and TM1 (located about 15 angstrom from d-glucose) are just as critical for transport as the residues that directly coordinate d-glucose, which demonstrates a strong allosteric coupling between sugar binding and gating. We conclude that PfHT1 has achieved substrate promiscuity not by modifying its sugar-binding site, but instead by evolving substrate-gating dynamics.

Crystal structure of the Plasmodium falciparum hexose transporter PfHT1 reveals the molecular basis of its ability to transport multiple types of sugar as efficiently as the dedicated mammalian glucose and fructose transporters.