Lee, T. M. | Search bioRxiv

bioRxiv2023

Mutational analysis of the nitrogenase carbon monoxide protective protein CowN reveals that a conserved C-terminal glutamic acid residue is necessary for its activity

Nitrogenase is the only enzyme that catalyzes the reduction of nitrogen gas into ammonia. Nitrogenase is tightly inhibited by the environmental gas carbon monoxide (CO). Many nitrogen fixing bacteria protect nitrogenase from CO inhibition using the protective protein CowN. This work demonstrates that a conserved glutamic acid residue near CowNs C-terminus is necessary for its function. Mutation of the glutamic acid residue abolishes both CowNs protection against CO inhibition and CowNs ability to bind to nitrogenase. In contrast, a conserved C-terminal cysteine residue is not important for CO protection. Overall, this work uncovers structural features in CowN that are required for its function and provides new insights into its nitrogenase binding and CO protection mechanism.

biochemistry↗

bioRxiv2023

Item-specific memory reactivation supports overnight memory consolidation

Memory consolidation stabilizes newly acquired information. Understanding how individual memories are reactivated during sleep is essential in theorizing memory consolidation. Via unobtrusively re-playing auditory memory cues to sleeping human participants, we identified the reactivation of individual memories during slow-wave sleep (SWS). Using representational similarity analysis (RSA) on cue-elicited electroencephalogram (EEG), we found functionally segregated item-specific representations: the early post-cue EEG activity (0-2 seconds) contained comparable representations for memory cues and for non-memory control cues, thus reflecting sensory processing. Critically, the later EEG activity (2.5-3 s) showed greater item-specific representations for post-sleep remembered items than for forgotten and control cues, demonstrating the reactivation and consolidation of individual memories. Moreover, spindles preferentially supported item-specific memory reactivation for items that were not tested before sleep. These findings delineated how cue-triggered item-specific memory reactivation, subserved by spindles during SWS, contributed to memory consolidation. These results will benefit future research aiming to perturb specific memory episodes during sleep.

neuroscience↗