Flecken, M. | Search bioRxiv

bioRxiv2020

Dual Role of a Rubisco Activase in Metabolic Repair and Carboxysome Organization

Rubisco, the key enzyme of CO2 fixation in photosynthesis, is prone to inactivation by inhibitory sugar phosphates. Inhibited Rubisco undergoes conformational repair by the hexameric AAA+ chaperone Rubisco activase (Rca) in a process that is not well understood. Here we performed a structural and mechanistic analysis of cyanobacterial Rca, a close homolog of plant Rca. In the Rca:Rubisco complex, Rca is positioned over the Rubisco catalytic site under repair and pulls the N-terminal tail of the large Rubisco subunit (RbcL) into the hexamer pore. Simultaneous displacement of the C-terminus of the adjacent RbcL opens the catalytic site for inhibitor release. An alternative interaction of Rca with Rubisco is mediated by C-terminal domains that resemble the small Rubisco subunit. These domains, together with the N-terminal AAA+ hexamer, ensure that Rca is packaged with Rubisco into carboxysomes. Cyanobacterial Rca is a dual-purpose protein with functions in Rubisco repair and carboxysome organization.

biochemistry↗

bioRxiv2019

Definitely saw it coming? An ERP study on the role of article gender and definiteness in predictive processing

People sometimes anticipate specific words during language comprehension. Consistent with word anticipation, pre-nominal articles elicit differential neural activity when they mismatch the gender of a predictable noun compared with when they match. However, the functional significance of this pre-nominal effect is unclear: Do people only predict the noun or do they predict the entire article-noun combination? We addressed this question in an event-related potential study (N=48) with pre-registered data acquisition and analyses, capitalizing on gender-marking on Dutch definite articles and the lack thereof on indefinite articles. Participants read mini-story contexts that strongly suggested either a definite or indefinite noun phrase (e.g., het/een boek, the/a book) as its best continuation, followed by a definite noun phrase with the expected noun or an unexpected, different gender noun ( het boek/de roman, the book/the novel). We observed an enhanced negativity (N400) for articles that were unexpectedly definite or mismatched the expected gender, with the former effect being strongest. Pre-registered analyses and exploratory Bayesian analyses did not yield convincing evidence that the effect of gender-mismatch depended on expected definiteness. While prediction of article form cannot be excluded, it may not be required to elicit pre-nominal effects.

neuroscience↗