Regulation of fibrillin carboxy-terminal furin processing by N-glycosylation, and association of amino- and carboxy-terminal sequences

The molecular mechanisms of fibrillin assembly into microfibrils are poorly understood. In this study, we investigated human fibrillin-1 carboxy-termi nal processing and assembly using a recombinant approach. Processing of car boxy-terminal fibrillin-1 was strongly influenced by N-glycosylation at the site immediately downstream of the furin site, and by association with cal reticulin, The carboxy terminus of fibrillin-2 underwent less efficient pro cessing than carboxy-terminal fibrillin-1 under identical conditions. Size fractionation of the amino-terminal region of fibrillin-1, and of unprocess ed and furin-processed carboxy-terminal region of fibrillin-1, revealed tha t the amino terminus formed abundant disulphide-bonded aggregates. Some ass ociation of unprocessed carboxy-terminal fibrillin-1 was also apparent, but processed carboxy-terminal sequences remained monomeric unless amino-termi nal sequences encoded by exons 12-15 were present. These data indicate the presence of fibrillin-1 molecular recognition sequences within the amino te rminus and the extreme carboxy-terminal sequence downstream of the furin si te, and a specific amino- and carboxy-terminal association which could driv e overlapping linear accretion of furin-processed fibrillin molecules in th e extracellular space. Differences in processing of the two fibrillin isofo rms may reflect differential abilities to assemble in the extracellular spa ce.