Premium
76
The Pneumocystis sam:smt, an atypical fungal enzyme protein
Author(s) -
Kaneshiro E. S.,
Basselin M.,
Yarbrough D. N.,
Smulian A. G.
Publication year - 2003
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.0022-3646.2003.03906001_76.x
Subject(s) - sterol , lanosterol , biology , biochemistry , enzyme , methyltransferase , ergosterol , recombinant dna , fungal protein , isomerase , sterol regulatory element binding protein , pneumocystis carinii , gene , methylation , cholesterol , saccharomyces cerevisiae , virology , pneumocystis jirovecii , human immunodeficiency virus (hiv)
Pneumocystis , an opportunistic fungal protist, causes a type of pneumonia in immunocompromised individuals such as AIDS patients. Rat‐derived P. carinii and human‐derived P. jiroveci contain a large number of sterols with C‐24 alkyl groups. S‐Adenosyl‐L‐methionine:sterol C‐24 methyl transferase (SAM:SMT) is the enzyme that transfers methyl groups from SAM to the C‐24 position of the sterol side chain. An alkyl group at the C‐24 sterol side chain position appears to be essential for the organism to proliferate. Thus SAM:SMT, which is absent in mammals, is an attractive target for chemotherapeutic attack against the pathogen. The P. carinii erg6 gene that codes for SAM:SMT has been sequenced, cloned, and the protein expressed in E. coli . Since bacteria do not synthesize sterols, and do not have SAM:SMT, the P. carinii erg6 gene product expressed in E. coli would only transmethylate exogenously provided sterol substrates. The P. carinii recombinant SAM:SMT is unique because lanosterol, a central intermediate in sterol biosynthesis, is its preferred substrate for enzyme activity. Most SAM:SMT from other organisms do not bind lanosterol and prefer other sterol substrates produced from lanosterol. Furthermore, it appears that this unusual P. carinii SAM:SMT can also methylate cholesterol, which is readily scavenged from the lungs of its rat host. The recombinant enzyme protein is being purified by affinity chromatography techniques, which will be used to obtain definitive structural analyses of the sterol compounds formed by the enzyme reaction using different sterols substrates and allow detailed structural analysis of this unusual SAM:SMT enzyme protein.