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Solution structures of human myeloma IgG3 antibody reveal extended Fab and Fc regions relative to the other IgG subclasses.

ABSTRACT: Human immunoglobulin G subclass 3 (IgG3) possesses a uniquely long hinge region that separates its Fab antigen-binding and Fc receptor-binding regions. Owing to this hinge length, the molecular structure of full-length IgG3 remains elusive, and the role of the two conserved Fc glycosylation sites are unknown. To address these issues, we subjected glycosylated and deglycosylated human myeloma IgG3 to multidisciplinary solution structure studies. Using analytical ultracentrifugation, the elongated structure of IgG3 was determined from the reduced sedimentation coefficients s⁰_20,w of 5.82 to 6.29 S for both glycosylated and deglycosylated IgG3. X-ray and neutron scattering showed that the Guinier R_G values were 6.95 nm for glycosylated IgG3 and were unchanged after deglycosylation, again indicating an elongated structure. The distance distribution function P(r) showed a maximum length of 25 to 28 nm and three distinct maxima. The molecular structure of IgG3 was determined using atomistic modeling based on molecular dynamics simulations of the IgG3 hinge and Monte Carlo simulations to identify physically realistic arrangements of the Fab and Fc regions. This resulted in libraries containing 135,135 and 73,905 glycosylated and deglycosylated IgG3 structures, respectively. Comparisons with the X-ray and neutron scattering curves gave 100 best-fit models for each form of IgG3 that accounted for the experimental scattering curves. These models revealed the first molecular structures for full-length IgG3. The structures exhibited relatively restricted Fab and Fc conformations joined by an extended semirigid hinge, which explains the potent effector functions of IgG3 relative to the other subclasses IgG1, IgG2, and IgG4.

SUBMITTER: Spiteri VA

PROVIDER: S-EPMC8371214 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND: Pregnant women remain are at an increased risk of malaria with primigravidae being at the highest risk. Genetic polymorphism of the Fc receptor IIa for immunologlobulin (Ig) G (Fc?RIIa) determines IgG subclass binding. Protection against pregnancy-associated malaria (PAM) is associated with the production of IgG specific for apical membrane antigen-1 (AMA-1). The present study was undertaken to examine the relationship between specific IgG/IgG subclasses and malaria infection. The second aim of the study is to examine the association between Fc?RIIa R/H131 polymorphism in correlation with specific anti-malarial IgG antibodies of AMA-1 distribution and asymptomatic malaria infection among Saudi women living in the southern part of Saudi Arabia. METHODS: One hundred and twenty pregnant women living in an area of meso-endemic Plasmodium falciparum malaria infection were consecutively enrolled onto the study. These pregnant women were asymptomatic and attending routine antenatal clinics. The levels of plasma antibodies (IgG and subclasses AMA-1) were measured using indirect enzyme-linked immunosorbent assays (ELISA). Genotyping of Fc?RIIa-R/H131 dimorphism was performed using gene-specific polymerase chain reaction (PCR) amplification with allele-specific restriction enzyme digestion (BstU1) of the PCR product. RESULTS: A total of sixty-two (52%) pregnant women was diagnosed with asymptomatic malarial infection (ASM) compared with 58 (48%) malaria free controls (MFC). In the ASM group, there were high levels of anti-malarial IgG1 and IgG3, when compared to MFC (P value <0.001, respectively). The Fc?RIIa-R/R131 genotype and R131 were found to be statistically significantly more prevalent in the ASM group when compared to the MFC group [55% for ASM versus 12% for MFC, odds ratio (OR) 5.62, 95% confidence interval (CI)= (2.03- 15.58), P value= 0.001]. However, the H/H131 genotype showed statistically significant association with MFC [14% for ASM versus 50% for MFC, OR(0.36), 95% CI= (0.14- 0.95), P value= 0.03]. CONCLUSIONS: The study revealed that the ASM patients had higher anti-malarial IgG and IgG subclasses antibody levels when compared to the MFC. The Fc?RIIa-R/R131 genotype and R131 allele were found to be statistically prevalent in the ASM when compared to the MFC group. The individuals carrying H/H131 were consistently associated with higher levels of anti-malarial IgG subclasses.

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Solution structures of human myeloma IgG3 antibody reveal extended Fab and Fc regions relative to the other IgG subclasses.

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