What is the structure of beta galactosidase?

Beta galactosidase is a 464 kDa tetramer molecule composed of 4 identical 1023-amino acid chains that form 4 active sites. Each chain is made up of 5 domains. Prominent domains include the TIM barrel domain followed by B-domain 1 and B-domain 2. The TIM barrel is formed by eight parallel beta strands and eight alpha helices. The arrangement creates a barrel-like structure where the beta strand forms the interior barrel and the alpha helices encompass the outside. This domain is essential for the enzyme’s ability to catalyze reaction and the active site primarily is located here. Domain 1 is structured as a jelly roll type barrel, which is made out of beta-strands arranged in a closed cylindrical shape. Domains 2 and 4 are fibronectin type III-like barrels. Fibronectin III domains generally consist of 8 antiparallel beta-strands which form a beta-sandwich structure. They assist in maintaining the stability and flexibility of the molecule. Domain 5 is a B-sandwich, in which beta strands fold against each other to form a beta-sandwich structure; however unlike domains 2 and 4 there are no certain amount of beta strands.