Chytrid Opsin structure paper published

Great work by former graduate student Steven Ahrendt (@sahrendt0), visiting student and current Duke graduate student Edgar Medina (@WhippingFungi) on the publication of a manuscript describing a Type II Opsin found in the zoosporic fungi.  “Exploring the binding properties and structural stability of an opsin in the chytrid Spizellomyces punctatus using comparative and molecular modeling” in PeerJ! Thanks also to co-author and collaborator Chia-en Chang in Chemistry Dept at UCR who helped mentor Steven on homology modeling and docking analyses. I also learned a lot through this project and was excited to be able to merge evolutionary and computational approaches. The project lead to the surprising findings of a gene important for light sensing that is shared among just the zoosporic (fungi with a flagellate life stage) and animals.

This project has been going for a while … Edgar and I discovered this protein in ~2008 when we started independently analyzing the Batrachochytrium genome, the first chytrid fungus sequenced. Based on sequence similarity we realized it looked like an animal rhodopsin, a 7 transmembrane G-protein coupled receptor (GPCR). These rhodopsins are called type II opsins and typically respond to green light.  We went looking for this in the first place because of work published in 1997 from Ken Foster’s lab which showed that zoosporic chytrid fungi respond to green light and that likely this behavior is due to a rhodopsin or rhodopsin-like GPCR  We found longer intact copy in the genome of the chytrid S. punctatus, so decided to focus on that copy – though we later discovered additional modifications of the predicted gene structure appeared necessary. We decided to do some homology modeling with the solved structure of a squid rhodopsin as shown in Figure 1. This confirmed that the sequence was compatible with the Type II Opsin structure. The paper documents several other computational simulations to test for the likely binding chromophore and hypothesis testing about the stability of the protein structure. Overall this work provides confidence that the sequence encoded in the genome of the zoosporic fungus can fold into a structure compatible with an opsin.

fig-1A
Figure 1A: Structural alignment of S. punctatus homology model (grey) with T. pacificus crystal structure (light purple)

It still remains to be tested if this opsin-like gene can biochemically function in this way. We hope to explore more of that with some additional work in the future. We have also nearly completed our manuscript analyzing the evolutionary history of this protein in fungi and related species to give a better picture of the timing of the emergence of this receptor-like protein. This project has helped advance some ideas about how zoosporic fungi interact with their environment based on genomic and computational analyses. This gene is a good candidate for future investigations into environmental sensing and signaling in zoosporic fungi.