Braun's lipoprotein (BLP, Lpp, murein lipoprotein, or major outer membrane lipoprotein), found in some gram-negative cell walls, is one of the most abundant membrane proteins; its molecular weight is about 7.2 kDa. It is bound at its C-terminal end (a lysine) by a covalent bond to the peptidoglycan layer (specifically to diaminopimelic acid molecules[1]) and is embedded in the outer membrane by its hydrophobic head (a cysteine with lipids attached). BLP tightly links the two layers and provides structural integrity to the outer membrane.
| Lipoprotein leucine-zipper | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | LPP | ||||||||
| Pfam | PF04728 | ||||||||
| InterPro | IPR006817 | ||||||||
| CATH | 1jccA00 | ||||||||
| SCOP2 | d1jcca_ / SCOPe / SUPFAM | ||||||||
| |||||||||
| Use IPR016367 for full protein. E. coli protein is P69776. | |||||||||
Characteristics
The gene encoding Braun's lipoprotein initially produces a protein composed of 78 amino acids, which includes a 20 amino acid signal peptide at the amino terminus.[2] The mature protein is 6 kDa in size.[3] Three monomers of Lpp assemble into a leucine zipper coiled-coil trimer.[4]
Large amounts of Braun's lipoprotein is present, more than any other protein in E. coli.[5] Unlike other lipoproteins, it is linked covalently to the peptidoglycan.[4] Lpp connects the outer membrane to the peptidoglycan. Lpp is anchored to the outer membrane by its amino-terminal lipid group. In E. coli, one third of Lpp proteins form a peptide bond via the side chain of its carboxy-terminal lysine with diaminopimelic acid in the peptidoglycan layer.[5][6] The rest of the Lpp molecules are present in a "free" form unlinked to peptidoglycan. The free form is exposed on the surface of E. coli.[3]
Functions
Lpp, along with another OmpA-like lipoprotein called Pal/OprL (P0A912), maintains the stability of the cell envelope by attaching the outer membrane to the cell wall.[3]
Lpp has been proposed as a virulence factor of Yersinia pestis, the cause of plague.[7] Y. pestis needs lpp for maximum survival in macrophages and to efficiently kill mouse models of bubonic and pneumonic plague.[8]
Immunology
Braun's lipoprotein binds to the pattern recognition receptor TLR2. Lpp induces adhesion of neutrophils to human endothelial cells by activating the latter.[9]