Soluble and bound acid protease activity of myelin from bovine cerebral white matter and spinal cord

Abstract

Isolated myelin of bovine spinal cord was found to degrade exogenous myelin basic protein (MBP) at pH 4.4. Electrophoretic peptide patterns were consistent with limited proteolysis of MBP. Some of the proteolytic activity was soluble at increased ionic strength, some remained bound, withstanding extraction at 37 degrees C for up to 12 hr. While being measurable with exogenous MBP, bound protease degraded neither bound MBP nor any other major intrinsic myelin protein. Both soluble and bound protease activity was completely inhibited by pepstatin A. The patterns of limited proteolysis of MBP they produced were identical. Myelin of cerebral white matter also exhibited soluble and bound acid protease activity which was likewise inhibited by pepstatin A. Protease activity of spinal cord and cerebral myelin is therefore suggested to be due to a cathepsin D-like endopeptidase, present in a loosely and tightly bound form. Both forms increased by 50 to 80% in activity when myelin was isolated from mixtures of white and cortical gray matter. While increased soluble activity of myelin is consistent with binding of cathepsin D of lysosomal origin during the isolation of myelin the tightly bound form might point to a principal mechanism through which exogenous proteins may become attached to the myelin sheath in vivo.

Mass‐spectrometric analysis of myelin proteolipids reveals new features of this family of palmitoylated membrane proteins

“…The presence of LMWPs in isolated myelin suggests that they are formed by the action of myelin‐associated proteases on PLP. Myelin is known to contain a series of proteolytic enzymes, including acid proteases (Berlet et al . 1988), calcium‐activated proteinase (Chakrabarti and Banik 1988), and metalloproteinases (Chantry et al .…”

“…The presence of LMWPs in isolated myelin suggests that they are formed by the action of myelin-associated proteases on PLP. Myelin is known to contain a series of proteolytic enzymes, including acid proteases (Berlet et al 1988), calcium-activated proteinase (Chakrabarti and Banik 1988), and metalloproteinases (Chantry et al 1989), any of which could be responsible for the cleavage of PLP at the intracellular loop. In addition, myelin contains several exopeptidases that could be responsible for some of the peptide trimming observed in this study (Hui et al 1988;Nagae et al 1992).…”