عنوان

Versicolorin B synthase:

شماره

TLpq304242433

زبان متن نوشتاري يا گفتاري و مانند آن

انگلیسی

عنوان اصلي

Versicolorin B synthase:

نام عام مواد

[Thesis]

نام نخستين پديدآور

J. C. Silva

عنوان اصلي به قلم نويسنده ديگر

Probing the aflatoxin B(1) biosynthetic pathway

نام ناشر، پخش کننده و غيره

The Johns Hopkins University

تاریخ نشرو بخش و غیره

1996

نام خاص و کميت اثر

305

جزئيات پايان نامه و نوع درجه آن

Ph.D.

کسي که مدرک را اعطا کرده

The Johns Hopkins University

امتياز متن

1996

متن يادداشت

Versicolorin B synthase (VBS) catalyzes the dehydrative cyclization of ()-versiconal hemiacetal (24) to the bisfuran ring system of ()-versicolorin B (25), an essential transformation in the aflatoxin biosynthesis by Aspergillus parasiticus owing to the mutagenic nature of aflatoxin B (1). The purification of native VBS facilitated the isolation of both cDNA and genomic clones of VBS to give a 1985 base genomic vbs DNA sequence interrupted by one intron of 53 nucleotides. Southern blotting, nucleotide sequencing and detailed restriction mapping of these clones supported the theory that the aflatoxin B biosynthetic genes in A. parasiticus are clustered. VBS, which shows 58% similarity and 38% identity with glucose oxidase from A. niger, possesses significant homology to the signature sequence of the GMC oxidoreductase family. The enzyme behaved as a dimer under non-denaturing conditions and migrated with usdM\sb{r}usd 78,000 under SDS-PAGE conditions. Comparisons to wild-type VBS by SDS-PAGE after PNGase F treatment revealed that extensive glycosylation accounted for the mass discrepency (7000 1500) between the native and inactive, bacterially-expressed VBS. Several expression systems in Saccharomyces cerevisiae were surveyed; one that incorporated a secretion signal (suc2) was found to be most successful. Yeast-derived VBS, of indistinguishable mass and kinetic properties to the wild-type enzyme, could be obtained in 50-100 fold greater amounts. Analysis of its pH-rate and stability profile suggested catalytic roles for one or two acidic residues (pKa = 3.7 0.1) and a basic residue (pKa = 7.3 0.1), a finding supported by chemical modification experiments suggesting the involvement of both aspartate and/or glutamate and histidine. Over-production of VBS in yeast marks the first aflatoxin biosynthetic enzyme to be so obtained and opens the way to direct study of the enzymology of this complex pathway.

موضوع مستند نشده

aflatoxin B

موضوع مستند نشده

Biochemistry

موضوع مستند نشده

Biological sciences

موضوع مستند نشده

Molecular biology

موضوع مستند نشده

Pure sciences

موضوع مستند نشده

sb1

مستند نام اشخاص تاييد نشده

J. C. Silva

نام الکترونيکي

فرمت انتشار

p

نوع ماده

[Thesis]

کد کاربرگه

276903

سطح دسترسي

a

تكميل شده

Y