Lipoma-preferred partner (LPP) protein localises to the cell periphery in focal adhesions and may play a structural role at sites of cell adhesion in maintaining cell shape and motility []. It may be involved in signal transduction from cell adhesion sites to the nucleus allowing successful integration of signals arising from soluble factors and cell-cell adhesion sites []. A chromosomal aberration involving LPP has been associated with several cancers [].
This entry represents the Major outer membrane lipoprotein (Lpp, also known as murein lipoprotein), which controls the distance between the inner and outer membranes [, ]. This abundant protein contains lipids in its N-terminal which anchor it to the outer membrane. This is the only protein known to bind covalently to the peptidoglycan network (PGN) but it also binds it through non-covalent interactions. About one-third of the Lpp is bound to the cell wall and the rest is free in the periplasm. Lpp have a structural function mediating the interactions between the outer membrane and PGN to assure the correct distance between them and contributes to the structural and functional integrity of the cell membrane []. The role of the periplasm free Lpp remains unknown.
This is leucine-zipper is found in the enterobacterial outer membrane lipoprotein LPP []. It is likely that this domain oligomerises and is involved in protein-protein interactions. As such it is a bundle of α-helical coiled-coils, which are known to play key roles in mediating specific protein-protein interactions for in molecular recognition and the assembly of multi-protein complexes [, , ].
Type 2 lipid phosphate phosphohydrolases (LPPs), formerly known as phosphatidic acid phosphatases (PAPs), are enzymes that catalyse the hydrolysis of a variety of lipid phosphate mono-esters, including lysophosphatidic acid (LPA), PA, diacylglycerolpyrophosphate, S1P and ceramide 1-phosphate (C-1-P). These are lipid mediators that exert complex effects on cell function through actions at cell surface receptors and on intracellular targets []. Type 2 LPPs are membrane bound enzymes, Mg2+-independent and N-ethylmaleimide-insensitive []. In humans, at least three genes coding for type 2 LPP enzymes have been identified (LPP1, LPP2 and LPP3).LPP1, also known as PPAP2A, exhibits a preference for glycerol-versus sphingoid base-containing lipids []. LPP1 plays a physiological role in controlling the degradation of circulating lysophosphatidic acid (LPA) [], a lipid mediator that stimulates cell proliferation and growth, and is involved in physiological and pathological processes such as wound healing, platelet activation, angiogenesis and the growth of tumours. LPP1 regulates LPA production and signaling in platelets [].
Type 2 lipid phosphate phosphohydrolases (LPPs), formerly known as phosphatidic acid phosphatases (PAPs), are enzymes that catalyse the hydrolysis of a variety of lipid phosphate mono-esters, including lysophosphatidic acid (LPA), PA, diacylglycerolpyrophosphate, S1P and ceramide 1-phosphate (C-1-P). These are lipid mediators that exert complex effects on cell function through actions at cell surface receptors and on intracellular targets []. Type 2 LPPs are membrane bound enzymes, Mg2+-independent and N-ethylmaleimide-insensitive []. In humans, at least three genes coding for type 2 LPP enzymes have been identified (LPP1, LPP2 and LPP3).This entry represents LPP2, also known as PPAP2C []. PPAP2C is overexpressed in several cancers. In cancer cells, PPAP2C is involved in S-phase progression and is regulated by p53 [].
Type 2 lipid phosphate phosphohydrolases (LPPs), formerly known as phosphatidic acid phosphatases (PAPs), are enzymes that catalyse the hydrolysis of a variety of lipid phosphate mono-esters, including lysophosphatidic acid (LPA), PA, diacylglycerolpyrophosphate, S1P and ceramide 1-phosphate (C-1-P). These are lipid mediators that exert complex effects on cell function through actions at cell surface receptors and on intracellular targets []. Type 2 LPPs are membrane bound enzymes, Mg2+-independent and N-ethylmaleimide-insensitive []. In humans, at least three genes coding for type 2 LPP enzymes have been identified (LPP1, LPP2 and LPP3).LPP3, also known as PPAP2B, is essential to the formation of the chorioallantoic placenta and extraembryonic vasculature. It also mediates gastrulation and axis formation, probably by regulating the Wnt signaling pathway []. A common PPAP2B polymorphism is associated with increased risk of coronary artery disease in humans [].
Members of this protein family are the TolB periplasmic protein of Gram-negative bacteria. TolB is part of the Tol-Pal (peptidoglycan-associated lipoprotein) multiprotein complex, comprising five envelope proteins, TolQ, TolR, TolA, TolB and Pal, which form two complexes. The TolQ, TolR and TolA inner-membrane proteins interact via their transmembrane domains. The β-propeller domain of the periplasmic protein TolB is responsible for its interaction with Pal. TolB also interacts with the outer-membrane peptidoglycan-associated proteins Lpp and OmpA. TolA undergoes a conformational change in response to changes in the proton-motive force, and interacts with Pal in an energy-dependent manner. The C-terminal periplasmic domain of TolA also interacts with the N-terminal domain of TolB. The Tol-PAL system is required for bacterial outer membrane integrity. Escherichia coli TolB is involved in the tonB-independent uptake of group A colicins (colicins A, E1, E2, E3 and K), and is necessary for the colicins to reach their respective targets after initial binding to the bacteria. It is also involved in uptake of filamentous DNA. Study of its structure suggests that the TolB protein might be involved in the recycling of peptidoglycan or in its covalent linking with lipoproteins. The Tol-Pal system is also implicated in pathogenesis of E. coli, Haemophilus ducreyi, Salmonella enterica and Vibrio cholerae, but the mechanism(s) is unclear.
