Hydrolyzes the 1,4-alpha-glycoside bonds in oligomeric and polymeric 1,4-alpha-glucans and transfers oligosaccharides (maltotriose being the shortest one) to acceptor maltodextrins. Transfers a segment of a (1->4)-alpha-D-glucan to a new position in an acceptor, which may be glucose or a (1->4)-alpha-D-glucan. Binds 1 Ca(2+) ion per subunit. Optimum pH is 7.0. Optimum temperature is 85 degrees Celsius. Monomer. Belongs to the glycosyl hydrolase 13 family.