Substitution of a single amino acid (aspartic acid for histidine) converts the functional activity of human complement C4B to C4A

Journal Article · Sat Sep 01 04:00:00 EDT 1990 · Proceedings of the National Academy of Sciences of the United States of America; (United States)

DOI:https://doi.org/10.1073/pnas.87.17.6868· OSTI ID:5452077

Carroll, M C; Fathallah, D M; Bergamaschini, L; Alicot, E M ^[1]; Isenman, D E ^[2]

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1. Harvard Medical School, Boston, MA (USA)
2. Univ. of Toronto, Ontario (Canada)

The C4B isotype of the fourth component of human complement (C4) displays 3- to 4-fold greater hemolytic activity than does its other isotype C4A. This correlates with differences in their covalent binding efficiencies to erythrocytes coated with antibody and complement C1. C4A binds to a greater extent when C1 is on IgG immune aggregates. The differences in covalent binding properties correlate only with amino acid changes between residues 1101 and 1106 (pro-C4 numbering)-namely, Pro-1101, Cys-1102, Leu-1105, and Asp-1106 in C4A and Leu-1101, Ser-1102, Ile-1105, and His-1106 in C4B, which are located in the C4d region of the {alpha} chain. To more precisely identify the residues that are important for the functional differences, C4A-C4B hybrid proteins were constructed by using recombinant DNA techniques. Comparison of these by hemolytic assay and binding to IgG aggregates showed that the single substitution of aspartic acid for histidine at position 1106 largely accounted for the change in functional activity and nature of the chemical bond formed. Surprisingly, substitution of a neutral residue, alanine, for histidine at position 1106 resulted in an increase in binding to immune aggregates without subsequent reduction in the hemolytic activity. This result strongly suggests that position 1106 is not catalytic as previously proposed but interacts sterically/electrostatically with potential acceptor sites and serves to select binding sites on potential acceptor molecules.

• OSTI ID: 5452077
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America; (United States), Journal Name: Proceedings of the National Academy of Sciences of the United States of America; (United States) Vol. 87:17; ISSN PNASA; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALANINES
AMINO ACIDS
ASPARTIC ACID
AUTORADIOGRAPHY
AZOLES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
COMPLEMENT
DAYS LIVING RADIOISOTOPES
DNA BASE TRANSITIONS
DNA SEQUENCING
DRUGS
ELECTROPHORESIS
EVEN-ODD NUCLEI
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HISTIDINE
IMIDAZOLES
ISOTOPES
LIGHT NUCLEI
LIPOTROPIC FACTORS
METHIONINE
NUCLEI
NUCLEIC ACIDS
OLIGONUCLEOTIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PLASMIDS
PROTEINS
RADIOISOTOPES
STRUCTURAL CHEMICAL ANALYSIS
SULFUR 35
SULFUR ISOTOPES