Involved in the degradation of arabinan and is a key enzyme in the complete degradation of the plant cell wall. Catalyzes the cleavage of endo alpha-(1->5)-L-arabinofuranosyl residues in debranched arabinan. Endohydrolysis of (1->5)-alpha-arabinofuranosidic linkages in (1->5)-arabinans. Binds 1 Ca(2+) ion per subunit. Optimum temperature is 70 degrees Celsius. The enzyme is stable for 30 minutes at temperatures up to 70 degrees Celsius. Glycan metabolism; L-arabinan degradation. Monomer. The N-terminal 16 amino acids plays an important role in the thermostability. Belongs to the glycosyl hydrolase 43 family.