Biology subjects

Knopp, M. R.

Publications and source records attributed to Knopp, M. R..

3 recordsLinked to original sources

bioRxiv2023

A mysterious cloak: the peptidoglycan layer of algal and plant plastids

The plastids of algae and plants originated on a single occasion from an endosymbiotic cyanobacterium at least a billion years ago. Despite the divergent evolution that characterizes the plastids of different lineages, many traits such as membrane organisation and means of fission are universal - they pay tribute to the cyanobacterial origin of the organelle. For one such trait, the peptidoglycan (PG) layer, the situation is more complicated, and little is known about its distribution and molecular relevance in green algae and land plants. Here, we investigate the extent of PG presence across the Chloroplastida using a phylogenomic approach. Our data support the view of a PG layer being present in the last common ancestor of land plants and its remarkable conservation across bryophytes that are otherwise characterized by gene loss. In embryophytes, the occurrence of the PG layer biosynthetic toolkit becomes patchier, but the availability of novel genome data questions previous predictions regarding a functional coevolution of the PG layer and the plastid division machinery-associated gene FtsZ3. Furthermore, our data confirm the presence of penicillin-binding proteins (PBPs) in seed plants, which were previously thought to be absent from this clade. The thicker and seemingly unchanged PG layer armouring the plastids of glaucophyte algae might still provide the original function of structural support, but the same can likely not be said about the only recently identified and ultrathin PG layer of bryophyte and tracheophyte plastids. In combination with the apparent lack of some genes thought critical for PG layer biosynthesis in land plants that, however, likely have a PG layer, this leaves many issues with respect to the composition, exact function, and biosynthesis in land plants to be explored.

evolutionary biology↗

bioRxiv2020

More than just a ticket canceller: The mitochondrial processing peptidase matures complex precursor proteins at internal cleavage sites

Most mitochondrial proteins are synthesized in the cytosol as precursors that carry N-terminal presequences. After import into mitochondria, these targeting signals are cleaved off by the mitochondrial processing peptidase MPP, giving rise to shorter mature proteins. Using the mitochondrial tandem protein Arg5,6 as a model substrate, we demonstrate that MPP has an additional role in preprotein maturation, beyond the removal of presequences. Arg5,6 is synthesized as a polyprotein precursor that is imported into the mitochondrial matrix and subsequently separated into two distinct enzymes that function in arginine biogenesis. This internal processing is performed by MPP, which cleaves the Arg5,6 precursor both at its N-terminus and at an internal site between the Arg5 and Arg6 parts. The peculiar organization and biogenesis of Arg5,6 is conserved across fungi and might preserve the mode of co-translational subunit association of the arginine biosynthesis complex of the polycistronic arginine operon in prokaryotic mitochondrial ancestors. Putative MPP cleavage sites are also present at the junctions in other mitochondrial fusion proteins from fungi, plants and animals. Our data suggest that, in addition to its role as “ticket canceller” for the removal of presequences, MPP exhibits a second, widely conserved activity as internal processing peptidase for complex mitochondrial precursor proteins.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biochemistry↗

bioRxiv2019

Major changes in plastid protein import and the origin of the Chloroplastida

While core components of plastid protein import (Toc and Tic) and the principle of using N-terminal targeting sequences (NTS) are conserved, lineage-specific differences are known. Rhodophytes and glaucophytes carry a conserved NTS motif, which was lost in the green lineage that also added novel proteins to Toc and Tic. Here we compare the components of plastid protein import and generated RNA-Seq, pigment profile and trans-electron microscopy data based on high-light stress from representatives of the three archaeplastidal groups. In light of plastid protein targeting, we compare the response to high-light stress of archaeplastidal representatives based on RNA-Seq, pigment profile and trans-electron microscopy data. Like land plants, the chlorophyte Chlamydomonas reinhardtii displays a broad respond to high-light stress, not observed to the same degree in the glaucophyte Cyanophora paradoxa or the rhodophyte Porphyridium purpureum. We find that only the green lineage encodes a conserved duplicate of the outer plastid membrane protein channel Oep80, namely Toc75 and suggest that the ability to respond to high-light stress entailed evolutionary changes in protein import, including the departure from phenylalanine-based targeting and the introduction of a green-specific Toc75 next to other import components unique to Chloroplastida. One consequence of relaxed NTS specificity was the origin of dual-targeting of plastid derived proteins to mitochondria and vice versa, using a single ambiguous NTS. Changes in the plastid protein import enabled the green lineage to import proteins at a more efficient rate, including those required for high-light stress response, a prerequisite for the colonization of land.\n\nHigh-lightsO_LILoss of Phe-based N-terminal targeting sequences (NTS) triggered the origin of dual-targeting using a single ambiguous NTS\nC_LIO_LIThe Chloroplastida evolved a green-specific Toc75 for high throughput import, next to a universal and ancient Omp85 present in all Archaeplastida\nC_LIO_LIA broad response to high-light stress appears unique to Chloroplastida\nC_LIO_LIRelaxation of functional constraints allowed a broader modification of the green Toc/Tic machinery\nC_LIO_LICritical changes in plastid targeting enabled the origin and success of the Chloroplastida and their later conquer of land\nC_LI

evolutionary biology↗