DNA repair: Locating and severing lethal links

Date:
August 27, 2020
Source:
Ludwig-Maximilians-Universita"t Mu"nchen
Summary:
Covalent cross-links between proteins and DNA are among the most
hazardous types of DNA damage. Researchers have now characterized
an enzyme that breaks such bonds, and elucidated how it specifically
recognizes sites of damage.



FULL STORY ========================================================================== Chemical lesions in the genetic material DNA can have catastrophic
consequences for cells, and even for the organism concerned. This
explains why the efficient identification and rapid repair of DNA damage
is vital for survival. DNA- protein crosslinks (DPCs), which are formed
when proteins are adventitiously attached to DNA, are particularly
harmful. DPCs are removed by the action of a dedicated enzyme --
the protease SPRTN -- which cleaves the bond between the protein and
the DNA. Up to now, how SPRTN recognizes such crosslinks, which can
differ significantly in structure, has remained unclear. Now a team led
by Professor Julian Stingele (LMU Gene Center), in cooperation with
Professor Michael Sattler (Helmholtz Zentrum Mu"nchen and Technical
University of Munich), has shown that the enzyme utilizes a modular
recognition mechanism to detect such sites, such that it is activated
only under highly specific conditions. The new findings appear in the
journal Molecular Cell.


==========================================================================
DPCs can be created by interactions with highly reactive products
of normal metabolism or with synthetic chemotherapeutic agents. These
lesions are extremely toxic because they block the replication of DNA --
and therefore inhibit cell division. Timely and effective repair of these crosslinks by SPRTN is crucial for cell viability and the suppression
of tumorigenesis. In humans, mutations that reduce the activity of the
enzyme are associated with a high incidence of liver cancer in early life
and markedly accelerate the aging process. "SPRTN has a difficult job
to do because, depending on the protein and the DNA subunit involved,
the structure of the crosslink can vary widely. So the enzyme has to be
able to identify many different structures as aberrant," explains Hannah Reinking, first author of the study. "We therefore asked ourselves what
sorts of properties a DPC should have in order to be recognized and
cleaved." To answer this question, Reinking and colleagues constructed
model substrates consisting of proteins attached to defined positions
within DNA strands, and examined whether the SPRTN protease could repair
them in the test-tube. This approach revealed that SPRTN interacts with structures that are frequently found in the vicinity of DPCs. With the
aid of nuclear magnetic resonance spectroscopy, they went on to show
that SPRTN contains two recognition domains.

One binds to double-stranded, and the other to single-stranded DNA. "So
the protein uses a modular system for substrate recognition. Only
when both domains are engaged is the enzyme active -- and DNA in which double-stranded and single-stranded regions occur in close proximity is
often found in the vicinity of crosslinks," says Stingele.

These results are also of clinical relevance. The action of many chemotherapeutic drugs depends on their ability to form crosslinks
with DNA.

Since tumor cells divide more frequently than non-malignant cells, they
are particularly sensitive to this type of DNA damage. DNA repair enzymes
like SPRTN are therefore of great interest as potential drug targets
for use in the context of personalized cancer therapies, and agents
that specifically inhibit the protease could eventually be employed to
boost the efficacy of chemotherapy. "Our work now makes it possible to conceptualize such therapeutic strategies," says Stingele.


========================================================================== Story Source: Materials provided by
Ludwig-Maximilians-Universita"t_Mu"nchen. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Hannah K. Reinking, Hyun-Seo Kang, Maximilian J. Go"tz, Hao-Yi
Li, Anja
Kieser, Shubo Zhao, Aleida C. Acampora, Pedro Weickert, Evelyn
Fessler, Lucas T. Jae, Michael Sattler, Julian Stingele. DNA
Structure-Specific Cleavage of DNA-Protein Crosslinks by the SPRTN
Protease. Molecular Cell, 2020; DOI: 10.1016/j.molcel.2020.08.003 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200827141339.htm

--- up 3 days, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)