细菌脂蛋白的合成流程：
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In Gram-negative bacteria, lipoproteins are synthesized as precursors with a N-terminal leader sequence (LS) carrying a cysteine-containing “lipobox.”[半胱氨酸的 "脂盒"]. Once transported through the inner membrane, the cysteine [半胱氨酸] is diacylated [二乙酰化] and lipoprotein precursors are cleaved upstream from the diacylated cysteine [二乙酰化半胱氨酸]. The free NH2 group of the cysteine is further acylated [酰化] and the triacylated lipoprotein [三酰化的脂蛋白] is finally transported to the outer membrane by the Lol transport machinery (16).
文献：Bacterial outer membrane vesicles engineered with lipidated antigens as a platform for Staphylococcus aureus vaccine
An outer membrane lipoprotein that controls the distance between the inner and outer membranes; adding residues to Lpp increases the width of the periplasm [外周胞质] (PubMed:29257832).
The only protein known to be covalently linked to the peptidoglycan network (PGN) [肽聚糖网络] (PubMed:4261992, PubMed:3013869, PubMed:4245367).
The link between the cell outer membrane and PGN contributes to the maintenance of the structural and functional integrity of the cell envelope, and maintains the correct distance between the PGN and the outer membrane (PubMed:4261992, PubMed:3013869, PubMed:4245367, PubMed:4565677).
The most abundant cellular protein in terms of copy number, there can be up to one million Lpp molecules per cell (PubMed:24766808).
About one-third of Lpp is bound to the PGN (called bound or periplasmic) the rest is called free or transmembrane (PubMed:4565677).
The 'free' form can be surface labeled by membrane impermeable agents and so must cross the outer membrane; it is thought that this transmembrane form is still anchored in the inner leaflet of the outer membrane (PubMed:21219470).
Modeling suggests that non-covalent binding of OmpA (from the outer membrane) and TolR (from the inner membrane) to peptidoglycan maintains the position of the cell wall in the periplasm, holding it approximately equidistant [ 等距 ] from both the inner and outer membranes.
Trimeric Lpp controls the width of the periplasm, adjusts its tilt angle to accommodate to the available space, and can compensate in part for an absence of OmpA (Probable). The role of the cell surface-exposed, free form (transmembrane) of Lpp is unknown (PubMed:21219470).
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Figure 1. Lipoproteins and outer membrane proteins are involved in OMV biogenesis. The Lpp, NlpI, OmpA, and Tol-Pal members maintain the stability of cellular envelopes [信封] joining the peptidoglycan layer [肽聚糖层] with the inner membrane. Interruption or deletion of the genes encoding these proteins decrease the number of linkages, inducing OMV formation. For example, mutation of the pal gene decreases linkage with the outer membrane, leading to membrane protrusion and OMV release. Additionally, the accumulation of components in the periplasm, such as peptidoglycan precursors, triggers vesicle formation.
Outer Membrane Vesicles of Gram-Negative Bacteria: An Outlook on Biogenesis
Type 3 secretion systems (T3SS)
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The type III secretion system (T3SS) is an important virulence device used by plant and animal pathogens to inject effectors upon contact with eukaryotic cells (Figure 1A).
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