Triacylglycerols sequester monotopic membrane proteins to lipid droplets

International audienceTriacylglycerols (TG) are synthesized at the endoplasmic reticulum (ER) bilayer and packaged into organelles called lipid droplets (LDs). LDs are covered by a single phospholipid monolayer contiguous with the ER bilayer. This connection is used by several monotopic integral membrane proteins, with hydrophobic membrane association domains (HDs), to diffuse between the organelles. However, how proteins partition between ER and LDs is not understood. Here, we employed synthetic model systems and found that HD-containing proteins strongly prefer monolayers and returning to the bilayer is unfavorable. This preference for monolayers is due to a higher affinity of HDs for TG over membrane phospholipids. Protein distribution is regulated by PC/PE ratio via alterations in monolayer packing and HD-TG interaction. Thus, HD-containing proteins appear to non-specifically accumulate to the LD surface. In cells, protein editing mechanisms at the ER membrane would be necessary to prevent unspecific relocation of HD-containing proteins to LDs

Lysozyme under holder pasteurized denaturation enhance the antioxidant's stability and quality attributes of functional yogurt

This research investigated the antioxidant activities and quality characteristics of functional yogurt supplemented with naturally derived protein, specifically lysozyme (LZ), as well as its thermally modified variants PLZ treated at 63°C for 30 minutes (hold type pasteurization method) and BLZ treated at 100°C for 10 minutes (using boiling temperature). Among these variants, the best antioxidant capacity was reported for PLZ, followed by BLZ and LZ. Subsequently, different yogurt samples (YCtrl, YLZ, YPLZ, and YBLZ) were prepared. Through weekly assessments, YPLZ consistently retained the highest antioxidant capacity. Moreover, YPLZ received the highest sensory evaluation scores with the best microbiological quality until the end of the examination period up to 35 days at 4 ±1°C. It was noted that PLZ displayed increased surface hydrophobicity due to gradual thermal denaturation, leading to structural changes and weak cross-dimerization with native milk alpha-lactalbumin in YPLZ. Gel electrophoresis results suggested that proteolysis by lactic acid bacteria (LAB) could facilitate the formation of low-molecular-weight peptides with enhanced antioxidant stability via weak-force dimerization. In conclusion, yogurt fortified with lysozyme, processed using hold-type pasteurization, presents a promising avenue for developing functional yogurt with antioxidant properties

Penetratin translocation mechanism through asymmetric droplet interface bilayers

International audiencePenetratin is a cell penetrating peptide (CPP) that can enter cells by direct translocation through the plasma membrane. The molecular mechanism of this translocation still remains poorly understood. Here we provide insights on this mechanism by studying the direct translocation of the peptide across model membranes based on Droplet Interface Bilayers (DIBs), which are bilayers at the interface between two adhering aqueous-in-oil droplets. We first showed with symmetric bilayers made of a mix of 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (POPG) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (POPC) that the translocation of penetratin required the presence of at least 40% of POPG on both leaflets. Interestingly when replacing POPG with another anionic lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (POPS), translocation was inefficient. To elucidate the lipid partners required at each step of the CPP translocation process, we then investigated the crossing of asymmetric bilayers. We found that POPG on the proximal leaflet and POPS on the distal leaflet allowed penetratin translocation. Translocation was not observed when POPS was on the proximal leaflet and POPG on the distal leaflet or if POPS on the distal leaflet was replaced with POPC. These observations led us to propose a three-step translocation mechanism: (i) peptide recruitment by anionic lipids, (ii) formation of a transient peptide-lipid structure leading to the initiation of translocation which required specifically POPG on the proximal leaflet, (iii) termination of the translocation process favored by a driving force provided by anionic lipids in the distal leaflet