Scanning tunnelling microscopy of Aspergillus niger glucoamylases

Gerard F.H. Kramer, A. Patrick Gunning, Victor J. Morris, Nigel J. Belshaw, Gary Williamson

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Abstract

The primary structure of glucoamylase 1 (glucan-1,4-α-glucosidase, EC 3.2.1.3) from Aspergillus niger consists of a catalytic and a binding domain separated by an O-glycosylated peptide 40 amino acid residues in length. Scanning tunnelling microscopic (STM) images of glucoamylase 2 (the catalytic domain with linker peptide) and a proteolytically cleaved product (the binding domain G1C, residues 471-616 of glucoamylase 1) confirmed that these proteins are globular and nearly spherical. Observed dimensions are: isolated catalytic domain (median half-height diameter, dm = 5.8 nm, 'in-plane' axial ratio, γ = 1.15:1), isolated binding domain (dm = 2.2 nm, γ = 1.18:1), catalytic domain within glucoamylase 1 (dm = 5.9 nm, γ = 1.1:1) and binding domain within glucoamylase 1 (dm = 3.4 nm, γ = 1.1:1). However, STM images of glucoamylase 1 suggest that the enzyme consists of two spatially separated globular domains. Measurements of the inter-domain spacing (median spacing between domain centres in glucoamylase 1, ds = 9.5 nm) suggest that the linker glycopeptide is extended and semi-rigid. These data suggest that the O-glycosylated sequence may play an important role in determining the shape and functionality of the enzyme.

Original languageEnglish
Pages (from-to)2595-2602
Number of pages8
JournalJournal of the Chemical Society - Faraday Transactions
Volume89
Issue number15
DOIs
Publication statusPublished - 1 Dec 1993
Externally publishedYes

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