Liam M. Longo

If you are an experimentalist interested in studying protein histories as a graduate student in the Longo Lab at ELSI, please get in touch!

Primitive nucleic acids and peptides likely collaborated in early biochemistry. What forces drove their interactions and how did these forces shape the properties of primitive complexes? We investigated how two model primordial polypeptides associate with DNA. When peptides were coupled to a ferromagnetic substrate, DNA binding depended on the substrate’s magnetic moment orientation. Reversing the magnetic field nearly abolished binding despite complementary charges. Inverting the peptide chirality or just the cysteine residue reversed this effect. These results are attributed to the chiral-induced spin selectivity (CISS) effect, where molecular chirality and electron spin alter a protein’s electric polarizability. The presence of CISS in simple protein–DNA complexes suggests that it played a significant role in ancient biomolecular interactions. A major consequence of CISS is enhancement of the kinetic stability of protein–nucleic acid complexes. These findings reveal how chirality and spin influence bioassociation, offering insights into primitive biochemical evolution and shaping contemporary protein functions.

The helix-hairpin-helix (HhH) motif is an ancient and ubiquitous nucleic acid-binding element that has emerged as a model system for studying the evolution of dsDNA-binding domains from simple peptides that phase separate with RNA. We analyzed the entire putative evolutionary trajectory of the HhH motif – from a flexible peptide to a folded domain – for functional robustness to total chiral inversion. Against expectations, functional ‘ambidexterity’ was observed for both the phase separation of HhH peptides with RNA and binding of the duplicated (HhH)2-Fold to dsDNA. Moreover, dissociation kinetics, mutational analysis, and molecular dynamics simulations revealed overlap between the binding modes adopted by the natural and mirror-image proteins to natural dsDNA. The similarity of several dissociation phases upon chiral inversion may reflect the history of (HhH)2-Fold binding, with the ultimate emergence of a high-affinity binding mode, supported by a bridging metal ion, depopulating but not displacing more primitive (potentially ambidextrous) modes. These data underscore the surprising functional robustness of the HhH protein family and suggest that the veil between worlds with alternative chiral preferences may not be as impenetrable as is often assumed.

If you are an experimentalist interested in studying protein histories as a graduate student in the Longo Lab at ELSI, please get in touch!

At the heart of many nucleoside triphosphatases is a conserved phosphate-binding sequence motif. A current model of early enzyme evolution proposes that this 6-8 residue motif could have sparked the emergence of the very first nucleoside triphosphatases – a striking example of evolutionary continuity from simple beginnings, if true. To test this provocative model, seven disembodied Walker A-derived peptides were extensively computationally characterized. Although dynamic flickers of nest-like conformations were observed, significant structural similarity between the situated peptide and its disembodied counterpart was not detected. Simulations suggest that phosphate binding is non-specific, with a preference for GTP over orthophosphate. Control peptides with the same amino acid composition but different sequences and situated conformations behaved similarly to the Walker A peptides, revealing no indication that the Walker A sequence is privileged as a disembodied peptide. We conclude that the evolutionary history of the P-Loop NTPase family is unlikely to have started with a disembodied Walker A peptide in an aqueous environment. The limits of evolutionary continuity for this protein family must be reconsidered. Finally, we argue that motifs such as the Walker A motif may represent incomplete or fragmentary molecular fossils – the true nature of which have been eroded by time.

Polyphosphate kinase 2 (PPK2) enzymes catalyze phosphoryl transfer from polyphosphate to nucleotides and are divided into three classes, each presumed to have different catalytic preferences. With relevance to biotechnology, medicine, and primitive biology, there is significant interest in understanding the evolutionary history of PPK2 enzymes and predicting their functional properties. We reasoned that the distribution and pairing preferences of PPK2 gene classes across the prokaryote tree of life may shed light on these questions. PPK2 was found to be a dynamic gene family, often present in only a subset of species within a clade, even when considering a single genus. Although all possible PPK2 pairs were observed, a ~2-fold enrichment for Class I enzymes in species with multiple PPK2 genes strongly shapes pairing preferences. PPK2 class preference in the absence of PPK1, which synthesizes rather than utilizes polyphosphate, indicates the potential for functional adaptation and/or promiscuity with respect to reaction directionality for all classes, a feature that has previously been associated only with Class I. Patterns of adjacent PPK2 genes revealed signatures of gene duplication, as adjacent genes overwhelmingly belonged to the same class, as well as the potential for an added layer of PPK2 dynamics: hetero-oligomerization of single-domain Class II enzymes to recapitulate the structure of two-domain Class II enzymes. Finally, an updated PPK2 tree constructed from domains instead of genes calls into question established narratives of PPK2 evolution, putting new limits on the extent to which nucleobase promiscuity can be invoked in the early evolution of this family.

In 1966, Margaret Dayhoff reasoned that duplication and fusion is a fundamental mechanism for generating protein complexity. Her insight inspired generations of scientists, several of whom would demonstrate this trajectory with short peptides that symmetrically assemble into a contemporary protein architecture. But how did these oligomerizing peptides, able to adopt complex conformations, emerge in the first place? In the present review, the evolution of an ancient and ubiquitous nucleic acid-binding element is traced from a simple, heterochiral peptide that coacervates with RNA to a folded-domain that binds with high affinity to the minor groove of double-stranded DNA.