Decrease in coccolithophore calcification and CO2 since the middle Miocene

International audienceMarine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone εp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity

The uronic acid content of coccolith-associated polysaccharides provides insight into coccolithogenesis and past climate

Unicellular phytoplanktonic algae (coccolithophores) are among the most prolific producers of calcium carbonate on the planet, with a production of ∼1026 coccoliths per year. During their lith formation, coccolithophores mainly employ coccolith-associated polysaccharides (CAPs) for the regulation of crystal nucleation and growth. These macromolecules interact with the intracellular calcifying compartment (coccolith vesicle) through the charged carboxyl groups of their uronic acid residues. Here we report the isolation of CAPs from modern day coccolithophores and their prehistoric predecessors and we demonstrate that their uronic acid content (UAC) offers a species-specific signature. We also show that there is a correlation between the UAC of CAPs and the internal saturation state of the coccolith vesicle that, for most geologically abundant species, is inextricably linked to carbon availability. These findings suggest that the UAC of CAPs reports on the adaptation of coccolithogenesis to environmental changes and can be used for the estimation of past CO2 concentrations

Exploring Fairness in Scholarly Development: Are We Creating Knowledge Storing Zombies or Curious, Creative and Critical Healthcare Professionals?

Charlotte R den Bakker,1 Arnout Jan de Beaufort,1 Friedo W Dekker,1,2 Belinda WC Ommering3 1Center for Innovation in Medical Education, Leiden University Medical Center, Leiden, the Netherlands; 2Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, the Netherlands; 3Research Centre for Learning and Innovation, Research Group on Research Competence, HU University of Applied Sciences Utrecht, Utrecht, the NetherlandsCorrespondence: Charlotte R den Bakker, Leiden University Medical Center, Center for Innovation in Medical Education, Hippocratespad 23, Zone V7-P, PO Box 9600, Leiden, 2333 ZD, the Netherlands, Tel + 31 71 52 998820, Email [email protected]: Scholarly doctors require research knowledge and skills (Ausbildung), as well as an academic mindset, which includes curiosity, creativity, and critical thinking (Bildung). However, in contrast to knowledge and skills, summative assessment of the development of an academic mindset is not so easy in an objective and so-called ‘fair’ way. As a result, in practice, assessing knowledge and skills tends to dominate in scholarly development. In this perspective, we explore the issues that arise when we give priority to objective assessment of knowledge and skills in scholarly development to safeguard fairness and, consequently, standardize educational procedures and learning pathways. We argue that eventually this approach may even result in hampered development of a true academic mindset and can be considered unfair rather than fair. To solve this, perhaps we should go back to the core business of the university and in the tradition of founder of the modern university Von Humboldt focus on shaping an academic mindset (Bildung). To rebalance Ausbildung and Bildung in academic education, we should go beyond the assumption that objectivity is a prerequisite for achieving fairness in assessment. Shifting the focus from pure objectivity to both objectivity and subjectivity in assessment as well as learning pathways can assist in protecting fairness and, as a result, bring back Bildung to medical education to ensure future doctors to be true scholars.Keywords: scholars, research training, Bildun

Mastering the canonical loop of serine protease inhibitors: Enhancing potency by optimising the internal hydrogen bond network

Background Canonical serine protease inhibitors commonly bind to their targets through a rigid loop stabilised by an internal hydrogen bond network and disulfide bond(s). The smallest of these is sunflower trypsin inhibitor (SFTI-1), a potent and broad-range protease inhibitor. Recently, we re-engineered the contact β-sheet of SFTI-1 to produce a selective inhibitor of kallikrein-related peptidase 4 (KLK4), a protease associated with prostate cancer progression. However, modifications in the binding loop to achieve specificity may compromise structural rigidity and prevent re-engineered inhibitors from reaching optimal binding affinity. Methodology/Principal Findings In this study, the effect of amino acid substitutions on the internal hydrogen bonding network of SFTI were investigated using an in silico screen of inhibitor variants in complex with KLK4 or trypsin. Substitutions favouring internal hydrogen bond formation directly correlated with increased potency of inhibition in vitro. This produced a second generation inhibitor (SFTI-FCQR Asn14) which displayed both a 125-fold increased capacity to inhibit KLK4 (Ki = 0.0386±0.0060 nM) and enhanced selectivity over off-target serine proteases. Further, SFTI-FCQR Asn14 was stable in cell culture and bioavailable in mice when administered by intraperitoneal perfusion. Conclusion/Significance These findings highlight the importance of conserving structural rigidity of the binding loop in addition to optimising protease/inhibitor contacts when re-engineering canonical serine protease inhibitors