Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2022.10.14.512171

TWO DISULFIDE-REDUCING PATHWAYS ARE REQUIRED FOR THE MATURATION OF PLASTID C-TYPE CYTOCHROMES IN CHLAMYDOMONAS REINHARDTII

Das, A.·Subrahmanian, N.·Gabilly, S. T.·Andrianova, E. P.·Jouline, I.·Motohashi, K.·Hamel, P. P.
View original source ↗Export metadata ↓

Abstract

AO_SCPLOWBSTRACTC_SCPLOWIn plastids, conversion of light energy into ATP relies on cytochrome f, a key electron carrier with a heme covalently attached to a CXXCH motif. Covalent heme attachment requires reduction of the disulfide bonded CXXCH motif by CCS5 and CCS4, a protein of unknown function. CCS5 receives electrons from the oxido-reductase CCDA at the thylakoid membrane. In Chlamydomonas reinhardtii, loss of CCS4 or CCS5 function yields a partial cytochrome f assembly defect. Here we report that the {Delta}ccs4ccs5 double mutant displays a synthetic photosynthetic defect due to a complete loss of holocytochrome f assembly, a phenotype that can be chemically corrected by reducing agents. In {Delta}ccs4, the CCDA protein accumulation is decreased, indicating that one function of CCS4 is to stabilize CCDA. Dominant suppressor mutations mapping to the CCS4 gene were identified in photosynthetic revertants of the {Delta}ccs4ccs5 mutants. The suppressor mutations correspond to changes in the stroma-facing domain of CCS4 and restore holocytochrome f assembly above the residual levels detected in {Delta}ccs5. Because disulfide reduction via CCS5 no longer takes place in {Delta}ccs5, we hypothesize the suppressor mutations enhance the supply of reducing power independently of CCS5, uncovering the participation of CCS4 in a distinct redox pathway. CCS4-like proteins occur in the green lineage and are related to mitochondrial COX16, a protein involved in a disulfide reducing pathway. We discuss the operation of two pathways controlling the redox status of the heme-binding cysteines of apocytochrome f and the possible function of CCS4 as a shared component between the two pathways. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=163 SRC="FIGDIR/small/512171v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@7f496forg.highwire.dtl.DTLVardef@ae5229org.highwire.dtl.DTLVardef@942b20org.highwire.dtl.DTLVardef@19b7576_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstract.C_FLOATNO The {Delta}ccs4ccs5 mutant exhibits a photosynthetic growth defect due to a complete loss of cytochrome c assembly. Reduction of apocytochrome f in the thylakoid lumen requires the provision of reducing power through two different pathways, pathway 1 and 2. CCDA and CCS5, components of pathway 1, deliver electrons from stroma to apocytochrome f via thiol - disulfide exchange. CCS4 is involved in pathway 1 by stabilizing CCDA, but also functions through a CCS5 - independent pathway (pathway 2). In the absence of CCS5, gain - of - function mutations in the C terminus of CCS4 (indicated by a yellow star) enhance the delivery of reducing power either via CCDA or independently of CCDA to yet-to-be-discovered reductases C_FIG

Explore related subjects

geneticsPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Das, A., Subrahmanian, N., Gabilly, S. T., Andrianova, E. P., Jouline, I., Motohashi, K., Hamel, P. P.. 2022-10-17. TWO DISULFIDE-REDUCING PATHWAYS ARE REQUIRED FOR THE MATURATION OF PLASTID C-TYPE CYTOCHROMES IN CHLAMYDOMONAS REINHARDTII. https://doi.org/10.1101/2022.10.14.512171

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Pangenome Discoveries from Clinical Long-Read Genomes in Underrepresented Populations with Neurodevelopmental Disorders

Genetic diagnoses remain elusive for many individuals with neurodevelopmental disorders (NDDs), and the gap is wider in populations poorly represented in genomic reference resources. To demonstrate the equitable advantage of long-read whole genome sequencing (LR-WGS) and pangenomes in terms of clinical utility, we analyzed 211 NDD cases and 107 unaffected relatives from 24 populations, integrating their assemblies, resulting in a total of 1204 haplotypes with the Human Pangenome Reference Consortium Release 2 (HPRC_r2) and the Arab Pangenome Reference (APR) datasets. Clinical interpretation of small variants and structural variants (SVs) revealed pathogenic or likely pathogenic findings in 38.9% of the cases (82/211), and our workflow further detected pathogenic repeat expansions in 3.8% of the cases and runs of homozygosity (ROHs) exceeding 300 Mb in 4.7% of the cases, revealing substantial autozygosity suggestive of strong inbreeding. Beyond these clinical assessments, pangenome analysis revealed 3.9 million population-level novel small variants, 39,782 SVs and an average of 2.17 Mb of novel sequence per individual absent from linear references and global pangenomes. We identified 85.9 kb of case-unique nonreference sequences in exonic segments overlapping with curated NDD gene sets. Graph-based tertiary analysis further identified rare exonic complex homozygous rearrangements in the NDD associated genes for 2.4% of the cases. Together, these findings emphasize how diverse genome assemblies extend variant discovery beyond established linear reference-based clinical interpretation.

genetics↗
bioRxiv2026

Integrated exome-transcriptome analysis of a schizophrenia case with an exceptionally low polygenic risk score

Schizophrenia liability reflects both common polygenic variation and rarer variants of larger effect. We investigated a post-mortem schizophrenia case (SZ07) with a schizophrenia polygenic risk score below the first percentile among ancestry-matched cases, asking whether individual-level genomic and transcriptomic analyses could help identify potentially novel schizophrenia-relevant variants. We used exome analysis with multiple variant-prediction tools to generate a panel of variants and corresponding candidate genes potentially implicated in the pathological process in SZ07. The prioritised variants were then assessed using RNA sequencing of three cortical regions. Of these, only an IZUMO4 splice-acceptor variant showed direct RNA-level support. Beyond variant-specific analyses, we characterised broader transcriptomic abnormalities in the SZ07 brain. Pathway analysis of gene-level expression deviations implicated innate immune processes, calcium signalling, synaptic biology, and axon remodelling. Notably, compared with conventional single-sample biological pathway analysis, the analysis we used showed only a weak association with neuronal specificity, suggesting their reduced sensitivity to the main axis of variation related to cellular composition in bulk brain tissue gene expression data. Although the candidate genes showed no significant pathway-level convergence, the broader transcriptomic profile revealed coherent biological alterations largely compatible with the documented history of cerebrovascular disease in SZ07. These results demonstrate how the integration of exome and transcriptome data at the individual level enables the formulation and constraint of hypotheses regarding patient-specific genetic features and their molecular consequences, while highlighting important limitations related to tissue composition, comorbidity, and the choice of reference cohort.

genetics↗
bioRxiv2026

A genetic screen to identify host factors required for commensal bacterial adherence to the gut epithelia

Bacterial adherence to gut epithelial cells likely involves host genetic components. We isolated a gut commensal bacterium, Lelliottia jeotgali, that can robustly colonize C. elegans through attachment to intestinal epithelial cells. Here, we developed a novel screen in C. elegans to identify host genes required for microbiome bacterial colonization. Using transgenic L. jeotgali strain expressing tdTomato, we conducted forward genetic screens in C. elegans to select for mutants that completely lost colonization. We identified multiple allelic mutations in five different C. elegans genes, termed knockout of Lelliottia adherence (kola) mutants, with a near complete loss of adherence. Each of kola-1-5 is uncharacterized and predicted to encode for a secreted or membrane-bound protein. We also identified gly-5, a GalNAc transferase that initiates O-linked glycosylation. Overall, we describe the first C. elegans screen to identify host factors that control microbiome bacterial colonization in the gut.

genetics↗