Biology subjects

Davies, P. L.

Publications and source records attributed to Davies, P. L..

8 recordsLinked to original sources

bioRxiv2025

Bioinformatic process for the identification and characterization of bacterial repeat-in-toxin adhesins

Gram-negative bacteria attach to host surfaces using ligand-binding domains (LBDs) at the distal tips of fibrillar RTX adhesins. Blocking the initial binding interaction(s) can potentially prevent colonization and subsequent biofilm formation and infection. To this end, adhesins must be identified, and it is also essential to determine the dominant adhesin type for those species that have more than one. RTX adhesins are frequently the largest proteins within each species (ranging from 1500 to 15,000 aa) and are often misannotated as incomplete/pseudogene products because their highly repetitive nature confounds genome assemblies from short-read technologies. Our bioinformatic process collates predicted proteins from long-read assemblies, which are then clustered based on the similarity of their C-terminal regions where the LBDs are typically located. RTX adhesins are identified by their length and domain structure and are modelled using AlphaFold3. An exhaustive search of multiple strains from seven species revealed a total of 35 different RTX adhesins that map to 16 different loci, with differing arrangements of LBDs that include putative carbohydrate-binding modules and von Willebrand Factor A-like domains. Notably, similar adhesins are sometimes found in multiple species, either by descent or through DNA uptake, and three species have an RTX adhesin of uncertain function because it lacks an obvious LBD. ImportanceMany bacteria initiate infection by reaching out with large, complex proteins called adhesins to attach themselves to a host cell. The DNA sequences of adhesins are difficult to read, due to their length and repetitiveness. This study leverages recent technological advances like "long-read sequencing" and structural modelling to identify and characterize the adhesins in seven species of harmful bacteria: Acinetobacter baumannii, Aeromonas hydrophila, Aeromonas salmonicida, Bordetella parapertussis, Legionella pneumophila, Vibrio parahaemolyticus, and Vibrio vulnificus. We identified thirty-five unique versions of adhesins and demonstrated their mix-and-match architecture. This research provides a foundation for strategies to block bacteria from binding surfaces, offering a vital alternative treatment as antibiotic resistance continues to rise.

biochemistry↗

bioRxiv2025

Peptide-based ligand antagonists block a Vibrio cholerae adhesin

Vibrio cholerae, the causative agent of cholera, uses surface proteins such as the repeats-in-toxin (RTX) adhesin FrhA to colonize hosts and initiate infection. Blocking bacterial adhesion represents a promising therapeutic strategy to treat infections without promoting drug resistance. FrhA contains a peptide-binding domain (PBD) that is key for hemagglutination, human epithelial cell binding, and V. cholerae biofilm formation. Previous studies identified a lead pentapeptide ligand with the sequence Ala-Gly-Tyr-Thr-Asp (AGYTD) that blocks V. cholerae colonization of the mouse small intestine at high micromolar concentrations. A structure-guided approach has now identified a minimal D-amino acid-containing tripeptide motif with higher affinity for the FrhA-PBD and predicted metabolic stability. Our results contribute to the development of anti-adhesion strategies to combat infections.

microbiology↗

bioRxiv2024

Convergent evolution of type I antifreeze proteins from four different progenitors in response to global cooling

The alanine-rich, alpha-helical type I antifreeze proteins (AFPs) in fishes are thought to have arisen independently in the last 30 ma on at least four occasions. This hypothesis has recently been proven for the flounder and sculpin AFPs that both originated by gene duplication and divergence followed by substantial gene copy number expansion. Here we have examined the origins of the cunner (wrasse) and snailfish (liparid) AFPs. The cunner AFP has arisen by a similar route from the duplication and divergence of a GIMAP gene. The coding region for this AFP stems from an alanine-rich region flanking the GTPase domain of GIMAPa. The AFP gene has remained in the GIMAP gene locus and undergone amplification there along with some GIMAPa genes. The AFP gene originated after the cunner diverged from the common ancestor to the closely related spotty and ballan wrasses that have a similar gene synteny but are completely lacking the AFP genes. Snailfish AFPs have also recently evolved because they are confined to a single genus of this family. In these AFP-producing species the AFP locus does not share any similarity to functional genes. Instead, it is replete with repetitive DNAs and transposons several stretches of which could code for tracts of alanine with a dominant codon (GCC) that matches the bias seen in the AFP genes. All four known instances of type I AFPs occurring in fishes are independent evolutionary events that happened soon after the onset of northern hemisphere Cenozoic glaciation events. Collectively they provide a remarkable example of convergent evolution to one AFP type.

molecular biology↗

bioRxiv2024

Human calpain-3 and its structural plasticity: dissociation of a homohexamer into dimers on binding titin

Calpain-3 is an intracellular Ca2+-dependent cysteine protease abundant in skeletal muscle. Its physiological role in the sarcomere is thought to include removing damaged muscle proteins after exercise. Loss-of-function mutations in its single-copy gene cause a dystrophy of the limb-girdle muscles. These mutations, of which there are over 500 in humans, are spread all along this 94-kDa multi-domain protein that includes three 40+-residue sequences (NS, IS1, and IS2). The latter sequences are unique to this calpain isoform and are hypersensitive to proteolysis. To investigate the whole enzyme structure and how mutations might affect its activity, we produce the proteolytically more stable 85-kDa calpain-3 {Delta}NS {Delta}IS1 form with a C129A inactivating mutation as a recombinant protein in E. coli. During size-exclusion chromatography, this calpain-3 was consistently eluted as a much larger 0.5-MDa complex rather than the expected 170-kDa dimer. Its size, which was confirmed by SEC-MALS, Blue Native PAGE, and AUC, made the complex amenable to single-particle cryo-EM analysis. From two data sets, we obtained a 3.85-[A] reconstruction map that shows the complex is a trimer of calpain-3 dimers with six penta-EF-hand domains at its core. Calpain-3 has been reported to bind the N2A region of the giant muscle protein titin. When this 37-kDa region of titin was co-expressed with calpain-3 the multimer was reduced to a 320-kDa particle, which appears to be the calpain dimer bound to several copies of the titin fragment. We suggest that newly synthesized calpain-3 is kept as an inactive hexamer until it binds the N2A region of titin in the sarcomere, whereupon it dissociates into functional dimers.

biochemistry↗

bioRxiv2023

Highly conserved, positively charged tandem repeats mediate multimerization of ice nucleation proteins

In nature, frost can form at a few degrees below 0 {degrees}C. However, this process requires the assembly of tens of thousands of ice-like water molecules that align together to initiate freezing at these relatively high temperatures. Water ordering on this scale is mediated by the ice nucleation proteins of common environmental bacteria like Pseudomonas syringae and P. borealis. However, individually, these 100-kDa proteins are too small to organize enough water molecules for frost formation, and it is not known how giant, megadalton-sized multimers, which are crucial for ice nucleation at high sub-zero temperatures, form. The ability of multimers to self-assemble was suggested when the transfer of an ice nucleation protein gene into Escherichia coli led to efficient ice nucleation. Here we demonstrate that a positively-charged sub-domain at the C-terminal end of the central beta-solenoid of the ice nucleation protein is crucial for multimerization. Truncation, relocation, or change of the charge of this subdomain caused a catastrophic loss of ice nucleation ability. Cryo-electron tomography of the recombinant E. coli showed that the ice nucleation protein multimers form fibres that are [~] 5 nm across and up to 200 nm long. A model of these fibres as an overlapping series of antiparallel dimers can account for all their known properties and suggests a route to making cell-free ice nucleators for biotechnological applications.

biochemistry↗

bioRxiv2022

Protein engineering shows antifreeze activity scales with ice-binding site area

The ice-binding site (IBS) of the 9.6-kDa springtail (Collembola) antifreeze protein from Granisotoma rainieri was identified by mutagenesis. We then studied the proteins activity as a function of IBS area. Its polyproline type II helical bundle fold facilitates changes to both IBS length and width. A one third increase in IBS width, through the addition of a single helix doubled antifreeze activity. A one third decrease in area reduced activity to 10%. A construct engineered with an additional tripeptide turn in each helix displayed a 5-fold decrease in activity. Molecular dynamics suggested that the lengthened IBS is more twisted than the wild type, emphasizing the importance of a flat surface for antifreeze activity.

biochemistry↗

bioRxiv2022

Chill injury in human kidney tubule cells after subzero storage is not mitigated by antifreeze protein addition

By preventing freezing, antifreeze proteins (AFPs) can permit cells and organs to be stored at subzero temperatures. As metabolic rates decrease with decreasing temperature, subzero static cold storage (SCS) could provide more time for tissue matching and potentially lead to fewer discarded organs. Human kidneys are generally stored for under 24 h and the tubule epithelium is known to be particularly sensitive to SCS. Here, telomerase-immortalized proximal-tubule epithelial cells from humans, which closely resemble their progenitors, were used as a proxy to assess the potential benefit of subzero SCS for kidneys. The effects of hyperactive AFPs from a beetle and Cryostasis Storage Solution were compared to University of Wisconsin Solution at standard SCS temperatures (4 {degrees}C) and at -6 {degrees}C for up to six days. Although the AFPs helped guard against freezing, lower storage temperatures under these conditions were not beneficial. Compared to cells at 4 {degrees}C, those stored at -6 {degrees}C showed decreased viability as well as increased lactate dehydrogenase release and apoptosis. This suggests that this kidney cell type might be prone to chilling injury and that the addition of AFPs to enable subzero storage may not be effective for increasing storage times.

cell biology↗

bioRxiv2021

Origin of the type I antifreeze gene in flounders in response to Cenozoic climate change

Antifreeze proteins (AFPs) inhibit ice growth within fish and protect them from freezing in icy seawater. Alanine-rich, alpha-helical AFPs (type I) have independently (convergently) evolved in four branches of fishes, one of which is a subsection of the righteye flounders. The origin of this gene family has been elucidated by sequencing two loci from a starry flounder, Platichthys stellatus, collected off Vancouver Island, British Columbia. The first locus had two alleles that demonstrated the plasticity of the AFP gene family, one encoding 33 AFPs and the other allele only four. In the closely related Pacific halibut, this locus encodes multiple Gig2 (antiviral) proteins, but in the starry flounder, the Gig2 genes were found at a second locus due to a lineage-specific duplication event. An ancestral Gig2 gave rise to a 3-kDa "skin" AFP isoform, encoding three Ala-rich 11-a.a. repeats, that is expressed in skin and other peripheral tissues. Subsequent gene duplications, followed by internal duplications of the 11 a.a. repeat and the gain of a signal sequence, gave rise to circulating AFP isoforms. One of these, the "hyperactive" 32-kDa Maxi likely underwent a contraction to a shorter 3.3-kDa "liver" isoform. Present day starry flounders found in Pacific Rim coastal waters from California to Alaska show a positive correlation between latitude and AFP gene dosage, with the shorter allele being more prevalent at lower latitudes. This study conclusively demonstrates that the flounder AFP arose from the Gig2 gene, so it is evolutionarily unrelated to the three other classes of type I AFPs from non-flounders. Additionally, this gene arose and underwent amplification coincident with the onset of ocean cooling during the Cenozoic ice ages.

evolutionary biology↗