Am. J. Respir. Crit. Care Med., Vol 150, No. 3, 09 1994, 823-832.
Identification of two major populations of mucins in respiratory secretions
DJ Thornton, PL Devine, C Hanski, M Howard and JK Sheehan
Division of Biochemistry, School of Biological Sciences, University of Manchester, UK.
Two populations of reduced subunits were present in the mucins purified
from pooled normal secretions and asthmatic and chronic bronchitic sputa;
their relative level differed between samples. To investigate the nature of
this heterogeneity, an asthmatic respiratory mucin preparation from a
single individual was reduced and alkylated with 14C- iodoacetamide. This
preparation was analyzed by gel filtration, agarose gel electrophoresis,
immunoblotting, rate-zonal- and density-gradient centrifugation, and HPLC
ion-exchange- and reverse-phase chromatography. Two populations (A and B)
of reduced mucin subunits and a high-M(r)protein-rich fraction were
identified. Species A has the higher molecular mass, is slowest migrating
on agarose electrophoresis, has longer oligosaccharide chains, and
expresses the carbohydrate structure sialyl-Le(x). Species B has a lower
molecular mass, migrates faster in agarose electrophoresis Species B has a
lower molecular mass, migrates faster in agarose electrophoresis, has
shorter chains, and does not express sialyl-Le(x). The two subunits have
similar but not identical amino acid compositions and 14C-tryptic peptide
maps indicating they have different protein cores. The anti-sialyl-Le(x)
antibody selectively precipitated subunit A not only from the reduced but
also from the nonreduced mucin preparation, demonstrating that subunits A
and B are present in different intact mucins.
