The Importance of Surface-Binding Site towards Starch-Adsorptivity Level in α-Amylase: A Review on Structural Point of View.

Umi Baroroh,Saadah Diana Rachman,Safri Ishmayana,Mas Rizky A A Syamsunarno,Jutti Levita,Muhammad Yusuf,Toto Subroto

doi:10.1155/2017/4086845

Abstract

Starch is a polymeric carbohydrate composed of glucose. As a source of energy, starch can be degraded by various amylolytic enzymes, including α-amylase. In a large-scale industry, starch processing cost is still expensive due to the requirement of high temperature during the gelatinization step. Therefore, α-amylase with raw starch digesting ability could decrease the energy cost by avoiding the high gelatinization temperature. It is known that the carbohydrate-binding module (CBM) and the surface-binding site (SBS) of α-amylase could facilitate the substrate binding to the enzyme's active site to enhance the starch digestion. These sites are a noncatalytic module, which could interact with a lengthy substrate such as insoluble starch. The major interaction between these sites and the substrate is the CH/pi-stacking interaction with the glucose ring. Several mutation studies on the Halothermothrix orenii, SusG Bacteroides thetaiotamicron, Barley, Aspergillus niger, and Saccharomycopsis fibuligera α-amylases have revealed that the stacking interaction through the aromatic residues at the SBS is essential to the starch adsorption. In this review, the SBS in various α-amylases is also presented. Therefore, based on the structural point of view, SBS is suggested as an essential site in α-amylase to increase its catalytic activity, especially towards the insoluble starch.

Highlights

Starch is the most abundant form of storage of many economically important crops such as wheat, rice, maize, tapioca, and potato [1, 2]
Carbohydrate-binding in such surface-binding sites, that is, SBSs, occurs in a fixed position relative to the catalytic site. It is different from the noncatalytic binding in carbohydrate-binding module (CBM), which are usually attached to the flexible loop structure [6]
The mCBM58 showed the highest activity to all substrates except for the insoluble cornstarch in which the activity was remarkably decreased up to 71%, whereas mSURF had the lowest activity for all substrates

Summary

Introduction

Starch is the most abundant form of storage of many economically important crops such as wheat, rice, maize, tapioca, and potato [1, 2]. About 10% of amylases contain a distinct noncatalytic module that is known to facilitate binding and degradation of raw starch [4]. The ability of the amylolytic enzyme to hydrolyze the raw starch was related to the level of starchadsorptivity properties [11]. Amylolytic enzymes with raw starch digesting ability may contain SBD and/or SBS. In this review, we focus on the importance of starch-binding SBSs. From a structural point of view, there are five examples of αamylases, with or without SBS, which can be used to review the following aspects: (1) the most significant factor in starchbinding, (2) the type of interactions that influence the binding of these proteins to the substrate in the noncatalytic module, and (3) the reason of low substrate adsorptivity to the protein despite having high amylolytic activities

Carbohydrate-Binding Module in Amylolytic Enzymes

C SBS III

Surface-Binding Site in α-Amylase

Findings

Conclusion