Biology subjects

Jackson, P. J.

Publications and source records attributed to Jackson, P. J..

3 recordsLinked to original sources

bioRxiv2024

Tethering ferredoxin-NADP+ reductase to photosystem I promotes photosynthetic cyclic electron transfer

Fixing CO2 via photosynthesis requires ATP and NADPH. Linear electron transfer (LET) supplies both metabolites, yet depending on environmental conditions, additional ATP is required which can be generated by cyclic electron transfer (CET). How the balance between LET and CET is set remains largely unknown. Ferredoxin(FD)-NADP+ reductase (FNR) has been suggested to act as the switch, channelling photosynthetic electrons to LET when it is bound to photosystem I (PSI) or CET when bound to cytochrome b6f. The essential role of FNR in LET precludes the use of a direct gene knock-out to test this hypothesis. We circumvented this problem by using CRISPR-Cas9 gene editing in Chlamydomonas reinhardtii to create a chimeric form of FNR tethered to PSI via PSAF. Chimeric FNR mutants exhibited impaired photosynthetic growth relative to the wild type, and decreased LET and non-photochemical quenching (NPQ) under high CO2 conditions. However, higher rates of CET and increased NPQ were found in the mutants under low CO2 or low O2 conditions where CET is normally up-regulated. Thus, rather than PSI-FNR interactions promoting LET, tethering FNR to PSI promotes CET at the expense of LET and CO2 fixation.

biochemistry↗

bioRxiv2022

Supercharged PGR5-dependent cyclic electron transfer compensates for mis-regulated chloroplast ATP synthase

The light reactions of photosynthesis couple electron and proton transfers across the thylakoid membrane, generating NADPH, and proton motive force (pmf) that powers the endergonic synthesis of ATP by ATP synthase. ATP and NADPH are required for CO2 fixation into carbohydrates by the Calvin-Benson-Bassham cycle (CBBC). The dominant {Delta}pH component of the pmf also plays a photoprotective role in regulating photosystem II (PSII) light harvesting efficiency, through non-photochemical quenching (NPQ), and cytochrome b6f (cytb6f) to photosystem I (PSI) electron transfer, via photosynthetic control. {Delta}pH can be adjusted by increasing the proton influx into the thylakoid lumen via upregulation of cyclic electron transfer (CET) or decreasing proton efflux via downregulation of ATP synthase conductivity (gH+). The interplay and relative contributions of these two elements of {Delta}pH control to photoprotection are not well understood. Here, we show that an Arabidopsis ATP synthase mutant (hope2) with 40% higher proton efflux, has supercharged CET. Double crosses of hope2 with the CET-deficient pgr5 and ndho lines reveal that PGR5-dependent CET is the major pathway contributing to higher proton influx. PGR5-dependent CET allows hope2 to maintain wild-type levels of {Delta}pH, CO2 fixation and NPQ, however photosynthetic control remains absent, and PSI is acceptor-side limited. Therefore, high CET in the absence of ATP synthase regulation is insufficient for PSI photoprotection.

plant biology↗

bioRxiv2020

Purification of recombinant SARS-CoV-2 spike, its receptor binding domain, and CR3022 mAb for serological assay

Serology testing for COVID-19 is highly attractive because of the relatively short diagnosis time and the ability to test for an active immune response against the SARS-CoV-2. In many types of serology tests, the sensitivity and the specificity are directly influenced by the quality of the antigens manufactured. Protein purification of these recombinantly expressed viral antigens [e.g., spike and its receptor binding domain (RBD)] is an important step in the manufacturing process. Simple and high-capacity protein purification schemes for spike, RBD, and CR3022 mAb, recombinantly expressed in CHO and HEK293 cells, are reported in this article. The schemes consist of an affinity chromatography step and a desalting step. Purified proteins were validated in ELISA-based serological tests. Interestingly, extracellular matrix proteins [most notably heparan sulfate proteoglycan (HSPG)] were co-purified from spike-expressing CHO culture with a long cultivation time. HSPG-spike interaction could play a functional role in the pathology and the pathogenesis of SARS-CoV-2 and other coronaviruses.

biochemistry↗