MUC5AC filaments illuminate the structural diversification of respiratory and intestinal mucins.

Secreted mucins are multimegadalton glycoprotein polymers that share the function of protecting mucosal tissues but diversified for activities in different organs of the body. Structural studies of secreted mucins are complicated by the enormous sizes, flexibility, and complex supramolecular assembly modes of these glycoproteins. The two major respiratory mucins are MUC5AC and MUC5B.