Glycoproteins of Aspergillus Fumigatus Cell Wall

Abstract

Most of the work done on Aspergillus cell wall has centered on the analysis of polysaccharidic structures. The major components have been identified as glucans and chitin with galactomannan as a minor constituent (Azuma et al.,1969). The protein content of the cell wall of those Aspergilli which have been studied is relatively low (Johnston, 1965; Bull, 1970 and Hearn and Mackenzie, 1979; Latgé et al., chapter 11). Pyridine extraction of a galactomannan-protein (APSK-66) from Aspergillus fumigatus mycelium has been reported (Azuma et al.,1968). The protein moiety was responsible for eliciting a delayed-type skin reactivity in both sensitized guinea pigs and rabbits while the carbohydrate moiety elicited an Arthus-type reaction (Suzuki and Hayashi, 1975). Molecules in situ on germ tube and mature hyphal surfaces have been used in indirect immunofluorescence tests as antigens to detect specific binding to anti-Aspergillus antibodies (Drouhet et al., 1972; Gordon et al.,1977; Schoenheyder et al., 1982). In similar tests, a germling surface antigen (Ag 5) has been used and identified as a non-ConA-binding, heat labile, protein molecule of apparent molecular mass (mol.mass.) of 34 kDa (Taylor and Longbottom, 1988). Recently, antibodies from patients with allergic bronchopulmonary aspergillosis (ABPA) were shown to bind specifically to antigens expressed on the surface of A. fumigatus spores and mycelium (Kurup et al., 1990). However, the chemical composition of these reactive surface antigens remains essentially undefined. The situation is further complicated by the known effects of age on the nature and distribution of cell wall components (Hunsley and Burnett, 1970; Barkai-Golan et al.,1978). Antigenic moieties of spore, germ-tube and hyphal structures have all been monitored and while common entities are found, marked differences have also been noted (Hearn, 1984.; John et al.,1984; Kauffman et al., 1984, Piechura et al., 1987). Recent EM studies have shown that most of the antigens recognized by antibodies from patients are localized in the mycelial cell wall (Fig.1) (Hearn et al., 1991). This result would reinforce the interest in studying cell wall glycoproteins.