A particulate insoluble fraction from Candida albicans J-1012 (serotype A) strain cells was obtained as the residue after extracting a 105,000 × g pellet of cell homogenate with 1% ~1 riton X-100. Incubation of this fraction with a mannopentaose, Man~l-->2Manotl-->(2Manal-Qz2Man (al~Mans), in the presence of GDP-mannose followed by high performance liquid chromatography showed the formation of a mannohexaose. Analysis of the product by ~H NMR indicates that a~Man5 was changed to Man~l--~ 2Manl~ll--~2Manal-~(2Manal--~)z 2Man (a~lMan6). This gl-l,2-mannosyltransferase (ManTase) II activity was completely inhibited by Zn 2÷ and was not restored by the addition of EDTA. The corresponding enzyme fraction from C. albieans NIH B-792 (serotype B) strain calls, the mannan of which does not possess both the otl3Mans and airMan6 side chains, also exhibited the same/3-1,2-ManTase II activity.
/(ey words: Candida albicans; fl-1,2-Linked mannose; Mannosyltransferase
~. IntroductionCandidiasis is an infectious disease frequently seen in early hildhood and in adults with predisposing conditions such as ,tiabetes, cancer, AIDS, and immuno-suppressive therapy [1,2]. Candida albicans strains were divided into two serotypes, A and ~, by Hasenclever and Mitchell [3] from the antigenicity of cell vall mannans. A structural study of the mannans of the 2 albicans serotype A and B strains has been achieved during he last several years [4,5], and we have demonstrated the pres-'nce of phosphodiesterified fl-l,2-1inked oligomannosyl moieies as a group of common epitopes throughout the two seroype strains [6,7]. The major difference between the structural !eatures of mannans from C. albicans serotype A and B strain .',ells is the presence of a fl-1,2-1inked mannose unit attached to m ~-l,2-1inked one in the side chains of the former mannan ,train [8,9], but lacking in the latter ones. We also reported in 'ecent papers that the serotype A-specific fl-1,2-1inked mannose mit in the mannans of C. albicans disappeared by cultivation )fthe cells under acidic pH [10] dida and several other yeasts. Thus, the detection of the circulating mannan antigen containing fl-l,2-1inkages in patients' sera by immunological procedures is important for the diagnosis of invasive candidiasis. Furthermore, several workers reported that the fl-1,2-linkage-containing side chains participate in adherence of C albicans cells to mammalian cells in the initial step of Candida infection [14,15]. Therefore, we tried to detect and characterize a fl-l,2-mannosyltransferase (ManTase) which is responsible for the biosynthesis of the serotype A specific epitope of C. albicans mannan. The biosynthetic pathway of the serotype A-specific side chain can be depicted as shown in Fig. 1 based on the structural analysis findings of C. albicans mannans [4]. Namely, the first transfer of the fl-l,2-linked mannose unit from GDP-mannose to the non-reducing terminal site of the ~-l,2-1inked mannotetraosyl side chain takes place by participation of the fl-l,2-ManTase I. However,...