Secretory proteins enter the ER lumen or, in case of transmembrane proteins, get inserted into the ER membrane. After proper folding and post-translational modifications, including N- and O-glycosylation and potential glycosylphosphatidylinositol (GPI) anchor addition, proteins are further modified in the Golgi and

packed in transport vesicles to convey them to the cell surface. Upon arrival at the cell membrane, transmembrane proteins and also some of the GPI proteins are retained. Other GPI proteins move further and become covalently attached to the wall via a truncated GPI anchor (Klis et al., 2002). Wall-bound GPI proteins are partially released into the medium BAY 80-6946 mw especially during growth-related remodeling of the cell wall. The soluble secretory proteins are released into the periplasmic region, from where most of them, except for some exceptionally large proteins (De Nobel et al., 1989), will diffuse into the environment. In this review, we define the predicted secretome as the set of secretory EX 527 proteins that have an N-terminal

signal sequence, including GPI proteins, but excepting proteins with internal transmembrane sequences, or an ER-targeting signal (Lum & Min, 2011). The measured secretome is then defined as the subset of proteins from the predicted secretome detected in the medium. Several computational studies have produced in silico estimates of the size of fungal secretomes (Lee et al., 2003; Liu et al., 2007; Swaim et al., 2008; Brustolini et al., 2009; Choi et al., 2010; Lum & Min, 2011). Here we use the estimates obtained by Lum & Min (2011). As expected, the size of the predicted secretome was found to be correlated with proteome size. The putative C. albicans secretome comprises c. 225 proteins (3.1% of the proteome), about 60 of which are predicted GPI proteins. Similar values (expressed as percentages) were obtained for the predicted secretomes of other species in the CTG clade, translating CTG as serine instead of leucine (Fitzpatrick et al., 2006; Candida dubliniensis 184, 3.1%; Candida guilliermondii 159, 2.7%; Candida lusitaniae 169, 2.8%; Candida tropicalis 212,

3.4%; Debaryomyces hansenii 148, 2.3%; Lodderomyces elongisporus 139, 2.4%). The predicted Thymidine kinase secretomes of yeasts from the Whole-Genome Duplication (WGD) clade (Fitzpatrick et al., 2006), like the pathogenic yeast Candida glabrata, and the nonpathogenic yeasts Kluyveromyces lactis, Pichia pastoris, Saccharomyces cerevisiae, and Schizosaccharomyces pombe tend to be slightly smaller than in the CTG clade comprising 121 (2.3% of the proteome), 113 (2.1%), 105 (2.1%), 156 (2.7%), and 112 (2.2%) secreted proteins, respectively. The predicted secretomes of saprophytic filamentous fungi are considerably larger than in yeasts, not only in absolute numbers but also expressed as percentage of the proteome: for example, 832 proteins (5.