carotenoids are associated with several important biological functions as antenna pigments in photosynthesis or protectives against oxidative stress. Occasionally they were also discussed as part of the cold adaptation mechanism of bacteria. For two Staphylococcus xylosus strains we demonstrated an increased content of staphyloxanthin and other carotenoids after growth at 10 °C but no detectable carotenoids after grow at 30 °C. By in vivo measurements of generalized polarization and anisotropy with two different probes Laurdan and TMA-DPH we detected a strong increase in membrane order with a simultaneous increase in membrane fluidity at low temperatures accompanied by a broadening of the phase transition. Increased carotenoid concentration was also correlated with an increased resistance of the cells against freeze-thaw stress. In addition, the fatty acid profile showed a moderate adaptation to low temperature by increasing the portion of anteiso-branched fatty acids. The suppression of carotenoid synthesis abolished the effects observed and thus confirmed the causative function of the carotenoids in the modulation of membrane parameters. A differential transcriptome analysis demonstrated the upregulation of genes involved in carotenoid syntheses under low temperature growth conditions. The presented data suggests that upregulated synthesis of carotenoids is a constitutive component in the cold adaptation strategy of Staphylococcus xylosus and combined with modifications of the fatty acid profile constitute the adaptation to grow under low temperature conditions. Carotenoids represent a large group and comprise at least 800 described compounds 1,2 which are synthesized from isoprene units by phototrophic and chemoorganotrophic prokaryotes, plants, fungi, and algae 3. Most carotenoids consist of eight isoprene units resulting in a C40 backbone and usually display β-cyclisation 1,4. Only a few chemoorganotrophic bacteria are capable of producing C30, C45 or C50 carotenoids 4,5. Such a rare C30 carotenoid is produced by staphylococci 6,7. As lipophilic compounds, carotenoids are located in the cell membrane, but their orientation inside the membrane may vary depending on their chemical structure and on the thickness of the membrane 8,9. They perform important biological functions such as light harvesting as antenna pigments 10,11 , provide protection against oxidative stress 5,12 , provide protection from ultraviolet radiation 13,14 , and stabilization of pigment proteins 15. In addition to the functions mentioned above, the involvement of carotenoids in cold adaptation was suspected 16-18. We assumed that carotenoids might have a similar function in regulating membrane fluidity as sterols such as cholesterol or ergosterol in eukaryotic cells. They increase membrane order with concurrent maintenance of lateral lipid motility, which results in a liquid-ordered membrane state 19. Similar mechanisms were previously described for the bacterial sterol-like hopanoids 20,21 and isoprenoid quinones 22. In vitro studies wit...

Oncogenic human papillomaviruses (HPV) are small DNA viruses that infect keratinocytes. After HPV binding to cell surface receptors, a cascade of molecular interactions mediates the infectious cellular internalization of virus particles. Aside from the virus itself, important molecular players involved in virus entry include the tetraspanin CD151 and the epidermal growth factor receptor (EGFR). To date, it is unknown how these components are coordinated in space and time. Here, we studied plasma membrane dynamics of CD151 and EGFR and the HPV16 capsid during the early phase of infection. We find that the proteinase ADAM17 activates the extracellular signal-regulated kinases (ERK1/2) pathway by the shedding of growth factors which triggers the formation of an endocytic entry platform. Infectious endocytic entry platforms carrying virus particles consist of two-fold larger CD151 domains containing the EGFR. Our finding clearly dissects initial virus binding from ADAM17-dependent assembly of a HPV/CD151/EGFR entry platform.

Profilins (PFNs) are key regulatory proteins for the actin polymerization in cells and are encoded in mouse and humans by four Pfn genes. PFNs are involved in cell mobility, cell growth, neurogenesis, and metastasis of tumor cells. The testes-specific PFN3 is localized in the acroplaxome–manchette complex of developing spermatozoa. We demonstrate that PFN3 further localizes in the Golgi complex and proacrosomal vesicles during spermiogenesis, suggesting a role in vesicle transport for acrosome formation. Using CRISPR/Cas9 genome editing, we generated mice deficient for Pfn3. Pfn3–/– males are subfertile, displaying a type II globozoospermia. We revealed that Pfn3–/– sperm display abnormal manchette development leading to an amorphous sperm head shape. Additionally, Pfn3–/– sperm showed reduced sperm motility resulting from flagellum deformities. We show that acrosome biogenesis is impaired starting from the Golgi phase, and mature sperm seems to suffer from a cytoplasm removal defect. An RNA-seq analysis revealed an upregulation of Trim27 and downregulation of Atg2a. As a consequence, mTOR was activated and AMPK was suppressed, resulting in the inhibition of autophagy. This dysregulation of AMPK/mTOR affected the autophagic flux, which is hallmarked by LC3B accumulation and increased SQSTM1 protein levels. Autophagy is involved in proacrosomal vesicle fusion and transport to form the acrosome. We conclude that this disruption leads to the observed malformation of the acrosome. TRIM27 is associated with PFN3 as determined by co-immunoprecipitation from testis extracts. Further, actin-related protein ARPM1 was absent in the nuclear fraction of Pfn3–/– testes and sperm. This suggests that lack of PFN3 leads to destabilization of the PFN3–ARPM1 complex, resulting in the degradation of ARPM1. Interestingly, in the Pfn3–/– testes, we detected increased protein levels of essential actin regulatory proteins, cofilin-1 (CFL1), cofilin-2 (CFL2), and actin depolymerizing factor (ADF). Taken together, our results reveal the importance for PFN3 in male fertility and implicate this protein as a candidate for male factor infertility in humans.

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