2 research outputs found
Crystal Structure of a Homogeneous IgG-Fc Glycoform with the N‑Glycan Designed to Maximize the Antibody Dependent Cellular Cytotoxicity
N-glycosylation
on IgG modulates Fc conformation and effector functions.
An IgG-Fc contains a human sialo-complex type (hSCT) glycan of biantennary
structure with two α2,6-sialylations and without core-fucosylation
is an optimized glycoform developed to enhance the antibody dependent
cellular cytotoxicity (ADCC). hSCT modification not only enhances
the binding affinity to Fc receptors in the presence of antigen but
also in some cases provides gain-of-function effector activity. We
used enzymatic glyco-engineering to prepare an IgG-Fc with homogeneous
hSCT attached to each C<sub>H</sub>2 domain and solved its crystal
structure. A compact form and an open form were observed in an asymmetric
unit in the crystal. In the compact structure, the double glycan latches
from the two hSCT chains stabilize the C<sub>H</sub>2 domains in a
closed conformation. In the open structure, the terminal sialic acid
(N-acetylneuraminic acid or NeuNAc) residue interacts through water-mediated
hydrogen bonds with the D249–L251 helix, to modulate the pivot
region of the C<sub>H</sub>2–C<sub>H</sub>3 interface. The
double glycan latches and the sialic acid modulation may be mutually
exclusive. This is the first crystal structure of glyco-engineered
Fc with enhanced effector activities. This work provides insights
into the relationship between the structural stability and effector
functions affected by hSCT modification and the development of better
antibodies for therapeutic applications
Role of N‑Linked Glycans in the Interactions of Recombinant HCV Envelope Glycoproteins with Cellular Receptors
Hepatitis C virus (HCV) infection
is a major cause of chronic hepatitis
and hepatocellular carcinoma. It infects human liver cells through
several cellular protein receptors including CD81, SR-BI, claudin-1,
and occludin. Previous reports also show that lectin receptors can
mediate HCV recognition and entry. The envelope proteins of HCV (E1
and E2) are heavily glycosylated, further indicating the possible
roles of lectin receptor–virus interaction in HCV infection.
However, there is limited study investigating the relationship of
HCV envelope glycoproteins and lectin as well as non-lectin receptors.
Here we used surface plasmon resonance to examine the binding affinity
of different glycoforms of recombinant HCV envelope protein to receptors
and inspected the infectivity and assembly of HCV pseudoparticles
composed of different glycoforms of envelope proteins. Our results
indicated that DC-SIGN, L-SIGN, and Langerin had higher affinity to
recombinant HCV envelope proteins in the presence of calcium ions
than non-lectin receptors, and envelope proteins with Man8/9 N-glycans
showed approximate 10-fold better binding to lectin receptors than
envelope proteins with Man5 and complex type N-glycans. Interestingly,
comparing among glycoforms, recombinant envelope proteins with Man5
N-glycans showed the highest binding affinity when interacting with
non-lectin receptors. In summary, the glycans on HCV envelope protein
play a modulatory role in HCV assembly and infection and direct HCV–receptor
interaction, which mediates viral entry in different cells. Receptors
with high affinity to HCV envelope proteins may be considered as targets
for development of a therapeutic strategy against HCV