The role of active site aromatic residues in substrate degradation by the human chitotriosidase.

Human chitotriosidase (HCHT) is a glycoside hydrolase family 18 chitinase synthesized and secreted in human macrophages thought be an innate part of the human immune system. It consists of a catalytic domain with the (β/α)8 TIM barrel fold having a large area of solvent-exposed aromatic amino acids in the active site and an additional family 14 carbohydrate-binding module. To gain further insight into enzyme functionality, especially the effect of the active site aromatic residues, we expressed two variants with mutations in subsites on either side of the catalytic acid, subsite -3 (W31A) and +2 (W218A), and compared their catalytic properties on chitin and high molecular weight chitosans.

The effect of the carbohydrate binding module on substrate degradation by the human chitotriosidase.

Human chitotriosidase (HCHT) is one of two active glycoside hydrolase family 18 chitinases produced by humans. The enzyme is associated with several diseases and is thought to play a role in the anti-parasite responses of the innate immune system. HCHT occurs in two isoforms, one 50 kDa (HCHT50) and one 39 kDa variant (HCHT39).

Analysis of productive binding modes in the human chitotriosidase.

Human chitotriosidase (HCHT) is a family 18 chitinase that is an innate part of the immune system. We have mapped preferred productive binding modes of chito-oligosaccharide substrates to HCHT and the data show that HCHT has strong binding affinity in the +3 subsite. Moreover, HCHT shows anomer-specific binding affinities in subsites +2 and +3.

Human chitotriosidase-catalyzed hydrolysis of chitosan.

Chitotriosidase (HCHT) is one of two family 18 chitinases produced by humans, the other being acidic mammalian chitinase (AMCase). The enzyme is thought to be part of the human defense mechanism against fungal parasites, but its precise role and the details of its enzymatic properties have not yet been fully unraveled. We have studied the properties of HCHT by analyzing how the enzyme acts on high-molecular weight chitosans, soluble copolymers of β-1,4-linked N-acetylglucosamine (GlcNAc, A), and glucosamine (GlcN, D).