Question

What are the domains and specific structures of alpha amylase? (both salvilary and pancreatic alpha amylase)

Answer 1

Domain and structure of salivary amylase

The salivary amylase is an important enzyme which is found in the oral cavity and belongs to the glycosidase family. The structures are present in the form of isoforms. It is a type of hydrolase which helps in breaking down complex carbohydrates into simple sugars. The enzymes consists of distinct domains or components like calcium ion, chloride ion and many other types of amino acids.

It consists of single polypeptide chain with 496 number of amino acids and the entire structure is divided into 3 domains.

Domain A – It consists of the active site of the enzyme along with three catalytic sites which are Asp197, Glu233 and Asp300. It also consists within it GLC sugars which helps in binding. There are hydrophobic ligands like Arg337, Arg195 and Asn298 which enables binding of the chloride ions. There are binding sites also containing hydrophobic residues which are Phe265 and Phe295 which again helps in enzyme catalytic activity.

Domain B- It consists of binding site for calcium. This domain binds to the calcium and stabilises the structure. It helps in holding the amino acid residues like Arg158, Asn100, Asp167 and His201 all in place.

Domain C- It is a beta structure and helps in compacting and holding the structure. However, the true function is yet to be known.

Domain and structure of pancreatic amylase

The structure of the pancreatic amylase consists of three types of structural domains:-

Domain A – It is the central domain which consists of eight stranded parallel beta-barrel and there are active sites located in it which are Asp 197, Glu 233, Asp 300. It also consists of a chloride ion which interactions with amino acid residues – Arg 195, Asn 298 and Arg 337.

Domain B – It is the smallest residue with total of 100 to 168 amino acid residues and it has a calcium binding site against the beta barrel structure that is present in the domain A. There are number of residues like Asn 100, Arg 158, Asp 167 and His 201.

Domain C – It consists total of 405 to 496 residues and made from anti-parallel beta structure. This domain is loosely associated with rest of the two domains.