Mucins are essential components in mucus gels that form protective barriers at all epithelial
surfaces, but much remains unknown about their assembly, intragranular organization, and
post-secretion unfurling to form mucus. MUC5B is a major polymeric mucin expressed by
respiratory epithelia, and we investigated the molecular mechanisms involved during its
assembly. Studies of intact polymeric MUC5B revealed a single high affinity calcium-binding
site, distinct from multiple low affinity sites on each MUC5B monomer. Self-diffusion studies …