The effect of myelin basic protein on the protease inhibitors alpha 1 antitrypsin and alpha 2 macroglobulin

Aberrant forms of alpha(2)-macroglobulin purified from patients with multiple sclerosis

The biochemical properties of alpha(2)-macroglobulin were investigated in four patients with multiple sclerosis and compared to alpha(2)-macroglobulin from healthy controls. An impaired stability of alpha(2)-macroglobulin from the multiple sclerosis patients was demonstrated as a spontaneous conversion to an electrophoretic"fast" form of alpha(2)-macroglobulin upon purification and storage, with a concomitant decrease in functional capacity to inhibit proteinases. The ability to form complexes with proteinases was significantly reduced in alpha(2)-macroglobulin purified from the multiple sclerosis patients. The aberrant molecular arrangements of the protein were not due to proteinase cleavages in the bait regions of alpha(2)-macroglobulin, as demonstrated by gel electrophoresis and protein sequencing. The number of functional thiol esters, however, was reduced in alpha(2)-macroglobulin purified from the multiple sclerosis patients, an observation compatible with the impaired proteinase binding property. Furthermore, differences in isoelectric points were observed between alpha(2)-macroglobulin from the multiple sclerosis patients and alpha(2)-macroglobulin from healthy controls. The results suggest that aberrant forms of alpha(2)-macroglobulin may be present in patients with multiple sclerosis.

Alpha-1-antitrypsin phenotypes and associated disease patterns in neurological patients

INTRODUCTION

Alpha-1-antitrypsin (AAT) deficiency is usually associated with lung or liver disease. It is often detected as a qualitative reduction of the alpha-1 band on the serum protein electrophoretic pattern.

MATERIAL AND METHODS

We examined the protein electrophoretic pattern in sera of 22980 unselected consecutive patients with neurological disorders and noted a reduced alpha-1 band in 88. Their phenotypes were compared with the clinical disease.

RESULTS

75 patients had a deficient or non-M and 13 the usual MM phenotype. Contrary to in the general population, PiMZ was four times more common than PiMS. Vascular disease was more common in patients with PiMZ while multiple sclerosis significantly more frequent in patients with PiMS than with other phenotypes, including PiMM.

CONCLUSIONS

Other genetic abnormalities have previously been found in AAT associated with multiple sclerosis, but not PiMS. Since PIMS leads to modest reduction of AAT activity, the association may be through other mechanisms than reduced protease activity.

Binding of lipoprotein lipase to alpha 2-macroglobulin

The interaction between bovine lipoprotein lipase (bLPL) and human alpha 2-macroglobulin (alpha 2M) was studied by use of non-denaturing PAGE and gel-permeation, Zn(2+)-Sepharose and heparin-Sepharose chromatography. It was demonstrated that bLPL in vitro binds non-covalently to native alpha 2M, but not to the receptor-recognized form produced by treatment of alpha 2M with chymotrypsin or methylamine. A small amount of bLPL was bound covalently to alpha 2M by disulphide interchange, when incubated together with chymotrypsin or methylamine. Whereas alpha 2M in complex with bLPL still bound to Zn(2+)-Sepharose, bLPL lost the ability to bind to heparin-Sepharose. Preincubation of bLPL with heparin prevented complex-formation with alpha 2M, suggesting that alpha 2M interacts with the heparin-binding domain of bLPL. Experiments in which 125I-bLPL was incubated with human plasma at 20 degrees C demonstrated an 11-17% binding of the labelled lipase to alpha 2M, indicating that this interaction may be of physiological significance.

Interaction and complex-formation between the eosinophil cationic protein and alpha 2-macroglobulin

The interaction between the highly basic and cytotoxic eosinophil cationic protein (ECP) and human plasma proteins is described. The major plasma protein responsible for complex-formation with ECP was shown to be the 'fast' form of alpha 2-macroglobulin (alpha 2M). Large amounts of complexes were observed in a serum obtained from a patient with hypereosinophilic syndrome. The amount of complexes that could be generated in vitro in normal fresh serum was rather low and was even less in fresh citrated plasma. Complex-formation between the non-proteolytic ECP and alpha 2M was augmented in the presence of methylamine. Binding of ECP to alpha 2M was also induced by the proteinases cathepsin G and thrombin, and the binding was competitive with cathepsin G. Methylamine and the proteinases seem to share a common mechanism in inducing binding of ECP. The nature of the ECP-alpha 2M interaction is non-covalent, but withstands high salt concentrations. The interaction with alpha 2M may reflect a mechanism by which the organism protects itself against the deleterious effects of the highly cytotoxic protein ECP.