Glycan specificity of a testis-specific lectin chaperone calmegin and effects of hydrophobic interactions.

Background: Testis-specific chaperone calmegin is required for the generation of normal spermatozoa. Calmegin is known to be a homologue of endoplasmic reticulum (ER) residing lectin chaperone calnexin. Although functional similarity between calnexin and calmegin has been predicted, detailed information concerned with substrate recognition by calmegin, such as glycan specificity, chaperone function and binding affinity, are obscure.

Trimming of glucosylated N-glycans by human ER α1,2-mannosidase I.

In the endoplasmic reticulum (ER), folding of proteins modified by asparagine-linked (N-linked) glycosylation is precisely monitored by quality control machinery. Upon exit from the calnexin/calreticulin cycle, glycoproteins are digested by α-mannosidases in the ER, especially α1,2-mannosidase I (ERManI). ERManI removes the α1,2-linked mannose of the B-chain from properly folded ER glycoproteins, whereas two or more α1,2-linked mannose residues are sequentially trimmed from improperly folded glycoproteins so they are recognized by a complex that mediates ER-associated degradation (ERAD).

In vitro mannose trimming property of human ER α-1,2 mannosidase I.

Endoplasmic reticulum α-1,2 mannosidase I (ERManI) is an enzyme, which removes α(1-2) linked mannoses from asparagine-linked oligosaccharides on glycoproteins in the endoplasmic reticulum (ER). ERManI preferentially removes one α(1-2) linked mannose from B-chain of Man(9)GlcNAc(2). When glycoproteins fail to achieve properly folding, increased removal of α(1-2) linked mannoses on their oligosaccharides is induced and leads them to be disposed and degraded by ER-associated degradation pathway.

Caenorhabditis elegans proteins captured by immobilized Galβ1-4Fuc disaccharide units: assignment of 3 annexins.

Galβ1-4Fuc is a key structural motif in Caenorhabditis elegans glycans and is responsible for interaction with C. elegans galectins. In animals of the clade Protostomia, this unit seems to have important roles in glycan-protein interactions and corresponds to the Galβ1-4GlcNAc unit in vertebrates.

Ligand-binding activity and expression profile of annexins in Caenorhabditis elegans.

Mammalian annexins are implicated in several physiological mechanisms based on their calcium-dependent phospholipid/membrane binding and carbohydrate-binding activities. In this study, we investigated gene expression profiles of all four Caenorhabditis elegans annexins, nex-1, -2, -3 and -4, throughout the development, and compared phospholipid- and carbohydrate-binding properties of their protein products, NEX-1, -2, -3 and -4. We found that nex-1 and -3 are transcribed continuously during the developmental stages, while expression of nex-2 and -4 appeared to be temporal, peaking at the L1 stage followed by a gradual decrease toward the adult stage.