Аннотация
APOBEC-2 (APO2) belongs to the family of apolipoprotein B mes-
senger RNA-editing enzyme catalytic (APOBEC) polypeptides,
which deaminates mRNA and single-stranded DNA 1,2 . Different
APOBEC members use the same deamination activity to achieve
diverse human biological functions. Deamination by an APOBEC
protein called activation-induced cytidine deaminase (AID) is crit-
ical for generating high-affinity antibodies 3 , and deamination by
APOBEC-3 proteins can inhibit retrotransposons and the replica-
tion of retroviruses such as human immunodeficiency virus and
hepatitis B virus 4–7 . Here we report the crystal structure of APO2.
APO2 forms a rod-shaped tetramer that differs markedly from the
square-shaped tetramer of the free nucleotide cytidine deaminase,
with which APOBEC proteins share considerable sequence homo-
logy. In APO2, two long a-helices of a monomer structure prevent
the formation of a square-shaped tetramer and facilitate forma-
tion of the rod-shaped tetramer via head-to-head interactions of
two APO2 dimers. Extensive sequence homology among APOBEC
family members allows us to test APO2 structure-based predic-
tions using AID. We show that AID deamination activity is
impaired by mutations predicted to interfere with oligomerization
and substrate access. The structure suggests how mutations in
patients with hyper-IgM-2 syndrome inactivate AID, resulting in
defective antibody maturation.
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