Braun's lipoprotein (BLP or Murein 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) 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.