Secretion, purification, and characterisation of barley α-amylase produced by heterologous gene expression in Aspergillus niger

N. Juge, B. Svensson, G. Williamson

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Efficient production of recombinant barley α-amylase has been achieved in Aspergillus niger. The cDNA encoding α-amylase isozyme 1 (AMY1) and its signal peptide was placed under the control of the Aspergillus nidulans glyceraldehyde-3-phosphate dehydrogenase (gpd) promoter and the A. nidulans trpC gene terminator. Secretion yields up to 60 mg/l were obtained in media optimised for α-amylase activity and low protease activity. The recombinant AMY1 (reAMY1) was purified to homogeneity and found to be identical to native barley AMY1 with respect to size, pI, and immunoreactivity. N-terminal sequence analysis of the recombinant protein indicated that the endogenous plant signal peptide is correctly processed in A. niger. Electrospray ionisation/mass spectrometry gave a molecular mass for the dominant form of 44,960 Da, in accordance with the loss of the LQRS C-terminal residues; glycosylation apparently did not occur. The activities of recombinant and native barley α-amylases are very similar towards insoluble and soluble starch as well as 2-chloro-4-nitrophenol β-D-maltoheptaoside and amylose (degree of polymerisation = 17). Barley α-amylase is the first plant protein efficiently secreted and correctly processed by A. niger using its own signal sequence.

Original languageEnglish
Pages (from-to)385-392
Number of pages8
JournalApplied Microbiology and Biotechnology
Issue number4
Publication statusPublished - 14 May 1998
Externally publishedYes

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