A short carboxyl-terminal tail is required for single-stranded DNA binding, higher-order structural organization, and stability of the mitochondrial single-stranded annealing protein Mgm101.
A short carboxyl-terminal tail is required for single-stranded DNA binding, higher-order structural organization, and stability of the mitochondrial single-stranded annealing protein Mgm101.
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DOI：
10.1091/mbc.e13-01-0006
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发表时间：
2013-05
影响因子：
3.3
通讯作者：
Chen XJ
中科院分区：
文献类型：
--
作者：
Mbantenkhu M;Wierzbicki S;Wang X;Guo S;Wilkens S;Chen XJ
Specific basic and aromatic amino acids in the C-terminal tail of Mgm101 play key roles in mediating ssDNA binding, stabilizing the oligomeric rings, and maintaining protein stability in vivo. The C-tail may couple ssDNA binding with ring disassembly, which facilitates the formation of nucleoprotein complexes competent for the repair of mtDNA. Mgm101 is a Rad52-type single-stranded annealing protein (SSAP) required for mitochondrial DNA (mtDNA) repair and maintenance. Structurally, Mgm101 forms large oligomeric rings. Here we determine the function(s) of a 32–amino acid carboxyl-terminal tail (Mgm101238–269) conserved in the Mgm101 family of proteins. Mutagenic analysis shows that Lys-253, Trp-257, Arg-259, and Tyr-268 are essential for mtDNA maintenance. Mutations in Lys-251, Arg-252, Lys-260, and Tyr-266 affect mtDNA stability at 37°C and under oxidative stress. The Y268A mutation severely affects single-stranded DNA (ssDNA) binding without altering the ring structure. Mutations in the Lys-251–Arg-252–Lys-253 positive triad also affect ssDNA binding. Moreover, the C-tail alone is sufficient to mediate ssDNA binding. Finally, we find that the W257A and R259A mutations dramatically affect the conformation and oligomeric state of Mgm101. These structural alterations correlate with protein degradation in vivo. The data thus indicate that the C-tail of Mgm101, likely displayed on the ring surface, is required for ssDNA binding, higher-order structural organization, and protein stability. We speculate that an initial electrostatic and base-stacking interaction with ssDNA could remodel ring organization. This may facilitate the formation of nucleoprotein filaments competent for mtDNA repair. These findings could have broad implications for understanding how SSAPs promote DNA repair and genome maintenance.
