Biology subjects

Upcher, A.

Publications and source records attributed to Upcher, A..

4 recordsLinked to original sources

bioRxiv2022

The Formation of Biogenic Guanine Crystals Closely Resembles Melanosome Morphogenesis

Animals precisely control the morphology and assembly of highly reflective guanine crystals to produce diverse optical phenomena used in coloration and vision. However, little is known about how organisms regulate crystallization to produce optically useful crystal morphologies which express highly reflective crystal faces. Guanine crystals form inside iridosome vesicles within specialized chromatophore cells called iridophores. By following the formation of iridosomes in developing scallop eyes we show that, despite their different physical properties, the morphogenesis of iridosomes bears a striking resemblance to melanosome morphogenesis in vertebrates. A key finding is that pre-assembled intravesicular fibrillar sheets template crystal nucleation, growth, and orientation, dictating the formation of optically functional, but thermodynamically disfavored plate-like habits. The common control mechanisms for melanin and guanine formation inspire new approaches for manipulating the morphologies and properties of molecular materials.

cell biology↗

bioRxiv2022

Asgard ESCRT-IIIs assemble into helical filaments in the presence of DNA and remodel eukaryotic membranes

The ESCRT machinery mediates membrane remodeling in numerous processes in cells including cell division and nuclear membrane reformation. The identification of ESCRT homologs in Asgard archaea, currently considered the closest ancestor of eukaryotes, implies a role for ESCRTs in the membrane remodeling processes that occurred during eukaryogenesis. Yet, the function of these distant ESCRT homologs is mostly unresolved. Here we show that Asgard ESCRT-III proteins of the Lokiarcheota self-assemble into helical filaments, a hallmark of the ESCRT system. We determined the cryo-EM structure of the filaments at 3.6 [A] resolution and found that they share features of bacterial and eukaryotic ESCRT-III assemblies. Markedly, Asgard ESCRT-III filaments bound and deformed eukaryotic-like membrane vesicles. Oligonucleotides facilitated the assembly of ESCRT-III filaments and tuned the extent of membrane remodeling. The ability of Asgard archaeal ESCRTs to remodel eukaryotic-like membranes, which are fundamentally different from archaeal membranes, and the structural properties of these proteins places them at the junction between prokaryotes and eukaryotes, substantiating a role for ESCRTs in eukaryogenesis. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=193 SRC="FIGDIR/small/506706v2_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@114999forg.highwire.dtl.DTLVardef@171a296org.highwire.dtl.DTLVardef@16931e0org.highwire.dtl.DTLVardef@1497c50_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2022

Natural Antimicrobial Peptides Self-assemble as α/β Chameleon Amyloids

Amyloid protein fibrils and some antimicrobial peptides (AMPs) share biophysical and structural properties. This observation suggests that ordered self-assembly can act as an AMP-regulating mechanism, and, vice versa, that human amyloids play a role in host defense against pathogens, as opposed to their common association with neurodegenerative and systemic diseases. Based on previous structural information on toxic amyloid peptides, we developed a sequence-based bioinformatics platform and, led by its predictions, experimentally identified 14 fibril-forming AMPs (ffAMPs) from living organisms, which demonstrated cross-{beta} and cross- amyloid properties. The results support the amyloid-antimicrobial link. The high prevalence of ffAMPs produced by amphibians and marine creatures among other species suggests that they confer unique advantageous properties in distinctive environments, potentially providing stability and adherence properties. Most of the newly identified 14 ffAMPs showed lipid-induced and/or time-dependent secondary structure transitions in the fibril form, indicating structural and functional cross-/{beta} chameleons. Specifically, ffAMP cytotoxicity against human cells correlated with inherent or lipid-induced -helical fibril structure. The findings raise hypotheses about the role of fibril secondary structure switching in regulation of processes, such as the transition between a stable storage conformation and an active state with toxicity against specific cell types.

biophysics↗

bioRxiv2022

Ontogenetic Color Switching in Lizards as a by-Product of Guanine Cell Development

Many animals undergo dramatic changes in colour during development1,2. Changes in predation risk during ontogeny are associated with spectacular switches in defensive colours, typically involving the replacement of skin or the production of new pigment cells3. Ontogenetic colour systems are ideal models for understanding the evolution and formation mechanisms of animal colour which remain largely enigmatic2. We show that defensive colour switching in lizards arises by reorganization of a single photonic system, as an incidental by-product of chromatophore maturation. The defensive blue tail colour of hatchling A. beershebensis lizards is produced by light scattering from premature guanine crystals in underdeveloped iridophore cells. Camouflaged adult tail colours emerge upon reorganization of the guanine crystals into a photonic reflector during chromatophore maturation. The substituent guanine crystals form by the attachment of individual nanoscopic plates, which coalesce during growth to form single crystals. Our results show that the blue colour of hatchlings is a fortuitous, but necessary, precursor to the development of adult colour. Striking functional colours in animals can thus arise not as distinct evolutionary innovations but via exploitation of the timing of naturally occurring changes in chromatophore cell development.

developmental biology↗