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Evidence for multiple sterol methyl transferase pathways in Pneumocystis carinii
Author(s) -
Zhou Wenxu,
Nguyen Thi Thuy Minh,
Collins Margaret S.,
Cushion Melanie T.,
Nes W. David
Publication year - 2002
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-002-1018-8
Subject(s) - lanosterol , sterol , ergosterol , phytosterol , fungus , campesterol , cycloartenol , biology , biochemistry , stigmasterol , steroid , stereochemistry , cholesterol , chemistry , botany , genetics , hormone
The sterol composition of Pneumocystis carinii , an opportunistic pathogen responsible for life‐threatening pneumonia in immunocompromised patients, was determined. Our purpose was to identify pathway‐specific enzymes to impair using sterol biosynthesis inhibitors. Prior to this study, cholesterol 15 ( ca. 80% of total sterols), lanosterol 1 , and several phytosterols common to plants (sitosterol 31 , 24α‐ethyl and campesterol, 24α‐methyl 30 ) were demonstrated in the fungus. In this investigation, we isolated all the previous sterols and many new compounds from P. carinii by culturing the microorganism in steroid‐immunosuppressed rats. Thirty‐one sterols were identified from the fungus (total sterol=100 fg/cell), and seven sterols were identified from rat chow. Unusual sterols in the fungus not present in the diet included, 24(28)‐methylenelanosterol 2 ; 24(28) E ‐ethylidene lanosterol 3 ; 24(28) Z ‐ethylidene lanosterol 4 ; 24β‐ethyllanosta‐25(27)‐dienol 5 ; 24β‐ethylcholest‐7‐enol 6 ; 24β‐ethylcholesterol 7 ; 24β‐ethylcholesta‐5,25(27)‐dienol 8 ; 24‐methyllanosta‐7‐enol 9 ; 24‐methyldesmosterol 10 ; 24(28)‐methylenecholest‐7‐enol 11 ; 24β‐methylcholest‐7‐enol 12 ; and 24β‐methylcholesterol 13 . The structural relationships of the 24‐alkyl groups in the sterol side chain were demonstrated chromatographically relative to authentic specimens, by MS and high‐resolution 1 H NMR. The hypothetical order of these compounds poses multiple phytosterol pathways that diverge from a common intermediate to generate 24β‐methyl sterols: route 1, 1→2→11→12→13 ; route 2, 1→2→9→10→13 ; or 24β‐ethyl sterols: route 3, 1→2→4→6→7 ; route 4, 1→2→5→8→7 . Formation of 3 is considered to form an interrupted sterol pathway. Taken together, operation of distinct sterol methyl transferase (SMT) pathways that generate 24β‐alkyl sterols in P. carinii with no counterpart in human biochemistry suggests a close taxonomic affinity with fungi and provides a basis for mechanism‐based inactivation of SMI enzyme to treat Pneumocystis pneumonia.