Biology subjects

Kirschbaum, C.

Publications and source records attributed to Kirschbaum, C..

6 recordsLinked to original sources

bioRxiv2026

YhdP forms an envelope-spanning phospholipid-binding bridge in complex with DedD

The outer membrane of Gram-negative bacteria is built from phospholipids synthesised at the inner membrane, but how they cross the periplasm remains unresolved. YhdP is the leading candidate for anterograde phospholipid transfer and is predicted to form an envelope-spanning bridge. Here we purify YhdP at endogenous levels and show by cryo-electron microscopy that it contains a continuous cavity, alongside an additional density that proteomics identifies as the cell wall-binding protein DedD. Liposome co-sedimentation shows that the C-terminal helices of YhdP bind membranes directly, and single-molecule tracking reveals that endogenous YhdP is as immobile as an outer membrane protein, indicating an envelope-spanning architecture in vivo. Native mass spectrometry demonstrates that the YhdP groove accommodates all major classes of E. coli phospholipid without headgroup preference. DedD engages YhdP through its disordered region and increases lipid density at the groove entrance, suggesting a potential role in lipid loading.

microbiology↗

bioRxiv2026

Defining state-selective lipid binding to brain GPCRs - introducing REVEAL

Membrane lipids are central regulators of G protein-coupled receptor (GPCR) function. Defining receptor-specific lipid interactions in native, fully modified mammalian systems remains challenging. Extensive post-translational modifications generate heterogeneous proteoforms that confound conventional mass spectrometry approaches. Here we introduce REVEAL (REceptor enVironment Elucidation by Activated Lipid-release), an automated native top-down mass spectrometry strategy that discriminates specifically bound lipids from background. Applied here to intact, heterogeneous mammalian membrane protein complexes, incubated with a brain polar lipid extract (>1000 components), we define receptor-specific lipid-binding for two neuronal class C GPCRs. We show that agonism remodels lipid occupancy, selectively enriching a reduced repertoire of bound lipids. Plasmalogen lipids emerge as persistent binders across all conformational states of the metabotropic glycine receptor and are preferentially depleted under oxidative stress, implying a protective role at the receptor surface. These findings position lipids as dynamic regulators of both function and response to the cellular redox environment.

biophysics↗

bioRxiv2026

Bifunctional Lipid-Protein Crosslinking Efficiency and Reaction Products

Bifunctional diazirine lipids are valuable tools for mapping protein-lipid interactions and cellular localization by photocrosslinking. Yet, the crosslinking efficiency of these probes has not been systematically evaluated. Here, we use the lipid transfer protein STARD10, which binds phospholipids in a 1:1 stoichiometry within a hydrophobic pocket, to measure the upper limit of the photo-crosslinking efficiency of bifunctional lipid probes. We characterize reaction products using native and denaturing mass spectrometry. Our results show that approximately 5% of photoactivated lipids form covalent protein-lipid crosslinks, while the majority follow intramolecular reaction trajectories, resulting in the formation of products featuring alkene, ketone and hydroxyl moieties. These findings provide essential context for the use of bifunctional probes to uncover the cell biology of lipids and highlight the need for continuous improvement to experimental workflows. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC="FIGDIR/small/700185v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@15d1641org.highwire.dtl.DTLVardef@6024e0org.highwire.dtl.DTLVardef@1503dcorg.highwire.dtl.DTLVardef@1b067bd_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2021

Dynamic behavior of cell-free mitochondrial DNA in human saliva

Mitochondria contain their own genome that can be released in multiple biofluids such as blood and cerebrospinal fluid, as cell-free mitochondrial DNA (cf-mtDNA). In clinical studies, single measures of blood cf-mtDNA predict mortality, and higher cf-mtDNA levels are associated with mental and physical stress. However, the dynamics of cf-mtDNA has not been defined, and whether it can be measured non-invasively like other neuroendocrine markers in saliva has not been examined. Here we report cf-mtDNA in human saliva and establish its natural within-person dynamic behavior across multiple weeks. In a small proof-of-principle cohort of healthy adults, we first develop an approach to rapidly quantify salivary cf-mtDNA without DNA extraction, and demonstrate the existence of saliva cf-mtDNA. We then deploy this approach to perform an intensive repeated-measures analysis of two healthy men studied at 4 daily timepoints over 53-60 consecutive days (n=212-220 observations each) with parallel measures of steroid hormones, self-reported daily mood, and health-related behaviors. Salivary cf-mtDNA exhibited a robust awakening response reaching up to two orders of magnitude 30-45 minutes after awakening, varied from day-to-day, and moderately correlated with the cortisol awakening response. No consistent association with self-reported daily mood/health-related behaviors were found, although this requires further examination in more extensive studies. Dynamic variation in cf-mtDNA was inversely related with salivary interleukin 6 (IL6), inconsistent with a pro-inflammatory effect of salivary cf-mtDNA. The highly dynamic behavior of salivary cf-mtDNA opens the door to non-invasive studies examining the relevance of mtDNA signaling in relation to human health.

molecular biology↗

bioRxiv2020

Contemplative mental training reduces hair glucocorticoid levels in a randomized clinical trial

ObjectiveThis study had the objective to investigate the effect of regular contemplative mental training on endocrine indices of long-term stress. MethodsAn open-label efficacy trial comprising three distinct 3-month modules targeting attention and interoception, socio-affective or socio-cognitive abilities through dyadic exercises and secularised meditation practices was designed and carried out in 332 healthy meditation-naive adults. Participants underwent the training for up to 9 months or were assigned to a retest control cohort. Chronic stress indices were assayed at four timepoints, i.e., pre-training and following each module. The main outcome measures were cortisol and cortisone concentration in hair and self-reported chronic stress ResultsN=362 initial individuals were randomized, of whom n=30 dropped out before study initiation, n=4 before first sampling and n=2 were excluded. N=99 participants did not provide hair samples. Data from three separate training cohorts revealed consistent decreases in hair cortisol and cortisone levels over the training period. This effect increased with practice frequency, was independent of training content and not associated with change in self-reported chronic stress. ConclusionsOur results point to the reduction of long-term cortisol exposure as a mechanism via which contemplative mental training may exert positive effects on practitioners health. Trial registrationClinicalTrials.gov identifier: NCT01833104

molecular biology↗

bioRxiv2020

Women show enhanced attractiveness ratings and neural processing of male faces associated with male chemosensory signals

There is growing evidence that humans use olfactory chemosensory signals for social communication, but their role in affective associative learning is largely unknown. To examine this, women implicitly learned face-odor associations by pairing different neutral male faces with either a male chemosignal presumably involved in human mating behavior (dissolved {Delta}4,16-androstadien-3-one, "AND"), a pleasant smell (dissolved vanillin) or the neutral solvent alone. After learning, women rated faces previously paired with AND or vanillin as more attractive than faces paired with solvent, even though they were unable to identify the contingency of face-odor pairings above chance level. On a neurophysiological level, both AND- and vanillin-associated faces evoked stronger magnetoencephalographic correlates of enhanced emotional attention than solvent-associated faces at early (<120 ms) and mid-latency (140-270 ms) processing stages. This study stresses the role of AND as a human chemosignal in implicit social communication and demonstrates its effectiveness in modulating emotional learning.

neuroscience↗