constant region – Ypatent

Introduction: Functions of Constant Domain

The constant domains are not involved directly in binding an antibody to an antigen, but mediate various effector functions based on their binding to cellular receptor or complement molecules.

Numberous evidences have shown that the antibody constant domain also plays a role in antibody antigen recognition. Antibodies with identical V regions differing in isotype or subclass manifest either differences in antigen binding, or altered specificity. (Zhao, “In silico methods in antibody design” Antibodies, 2018)

Structure of the Constant Region

A full lenght immunoglobulin heavy chain is a polypeptide consisting in N-terminal to C-terminal direction an immunoglobulin constant domain 1 (CH1), an immunoglobulin hinge region, an immunoglobulin constant domain 2 (CH2), an immunoglobulin constant domain 3 (CH3) and optionally an immunoglobulin constant domain 4 (CH4) in the case of an immunoglobulin of the subclass IgE.

Hinge region: is located between the CH1 and CH2 domains. Both the hinge region and the tail (Fc) region are formed by the two heavy chains. It generally stretches from Glu216 to Pro230 of human IgG1. The efficiency of antigen binding and cross-linking is greatly increased by a flexible hinge region in the heavy chains of the 3 classes, IgG, IgD and IgA. The hinge region is particularly sensitive to proteolytic cleavage yielding 2-3 fragments depending on the precise site of cleavage.

“Hinge” or “hinge region” is means the flexible polypetpide including the amino aicds between the frist and second constant domains (CH1 and CH2) of an antibody. It includes residues 216-230. (Zhang, WO 2017/034770)

CH1 domain: refers to the H chain immunoglobulin constant domain located between VH domain and the hinge. It spans EU positions 118-215. (Villanueva, US 16/470,533, published as US 2020/0157190)

Hinge region: is generally defined as stretching from Glu216 to Pro230 of human IgG1. Hinge regions of other IgG isotypes may be aligned with the IgG1 sequence by placing the first and last cystein residues forming inter-heavy chain SS-bonds in the same positions. (Giese, US 16/221,369 published as US 2019/0256556).

Fc Domain:

Immunoglobulins are composed of two heavy and two light chains, each of which contains an NH2 terminal antigen-binding variable domain and a CooH terminal constant domain responsible for the effector functions of antibodies. The COOH temminal domains of the Ig heavy chains form the Fc region and are involved in triggering cellular activities trhough interaction with specific receptors known as Fc receptors. FcRs exists all Ig classes, or isotypes. (WO96/40789)

The part of the heavy chain constant region containing the CH2 and CH3 domains is called the “Fc” part of the immunoglobulin. Antibodies are thus Fc-containing proteins. The human IgG heavy chain Fc region is usually defined to stretch from an amino acid residue at position Cys226 or from Pro230 to the carboxyl-terminus.

“Fc” or “Fc region” or Fc fragment” is used to mean polypeptides that include at least two constant immunoglobulin domains (CH2 and CH3) of IgA, IgD and IgG and the last threee constant region immunoglobulin domains of IgE and IgM, and part of the flexible hinge N-temrinal to these domains. Although the boundaries of the Fc reigon may vary, the human IgG H Fc region is usually defined to include residues starting at A231 to its carboxyl-temrinus, wherein the numbering is according to the EU numbering scheme. (Zhang, WO 2017/034770).

CH2 domain: of human IgG Fc region usually extends from about amino acid 231 to about amino acid 340. The CH2 domain is unique in that it is not closely paired with another domain. Rather, two N-linked branched carbohydrate chains are interposed between the two CH2 domains of an intact native IgG molecule. (Giese, US 16/221,369 published as US 2019/0256556)

The CH2 domain refers to the H chain immunoglobulin constant domain that is located between the hinge and the CH3 domain. It spans EU positions 237-340. (Villanueva, US 16/470,533, published as US 2020/0157190)

CH3 domain: comprises the stretch of residues C terminal to a CH2 domain in an Fc region from about residues 341 to about 447 of an IgG. (Giese, US 16/221,369 published as US 2019/0256556)

The CH3 domain refers to the H chain immunogloublin constant domain that is located C terminally of the CH2 domain and spans about 110 residues from the N-terminus of the CH2 domain (e.g., about positions 341-446b (EU numbering system). (Villanueva, US 16/470,533, published as US 2020/0157190)