of the Max - MDC

A
B
Figure 2. Palmitoylation of the TRAPP subunit Bet3 at cysteine 68. (A) Similar amounts of GST-tagged wildtype Bet3 and single-site
mutants with replacements of residues A82, C68 and R67 (left) were incubated with [ 3 H]-palmitoyl CoA. The fluorograms (right) show that
palmitoylation is strictly dependent on the presence of cysteine at position 68 and significantly reduced by a channel-blocking mutation at
position 82 or a charge-reversal as position 67. (B) The palmitoyl chain resides in a deep channel on the Bet3 surface which can be blocked
by introducing bulky sidechains at position 82.
5,10-Methenyltetrahydrofolate synthetase (MTHFS) catalyzes
the first metabolic step in the conversion of folinic
acid to reduced folates which serve as donors of one-carbon
units in various anabolic reactions. MTHFS regulates folatedependent
reactions involved in cell growth and development
which are crucial for cancer treatment and prevention.
The crystal structure of human MTHFS was determined in
two distinct forms: In both, as well as in solution, the
human enzyme is monomeric whereas its bacterial
homologs are dimeric. The substrates, folinic acid and ATP,
bind in two separate pockets connected by a tunnel. In
cooperation with the Berlin-Buch Screening Unit, two
MTHFS inhibitors could be identified whose mode of binding
is currently under investigation by co-crystallization and
structure analysis.
β-Sheet proteins as models for amyloid
aggregation
Jürgen J. Müller
A large and growing set of human and veterinary diseases
are associated with intra- or extracellular deposits of aggregated
protein. These protease-resistant protein deposits are
predominantly β-structured. There is rapidly accumulating
evidence that many proteins have the propensity to undergo
structural transitions from a globular and soluble physiological
form to an insoluble and disease-associated cross-β
conformation. Unfortunately, the β-structured aggregates
are not amenable to high-resolution structure analyses.
Globular protein structures with repetitve β-structure are of
interest, since they may highlight important properties of
the cross-β amyloid conformation. The trimeric bacteriophage
tailspike proteins (TSP) contain a large central
domain displaying a regular right-handed β-helix fold. We
have determined the crystal structures of phage Sf6 TSP and
of phage HK620 TSP at high resolution. Their β-helix
domains are best described as coiled β-coils; in Sf6 TSP the
β-helices intertwine to form a left-handed superhelix with a
pitch of 47 nm. The structures of the two TSP help to define
the sequence patterns giving rise to repetitive β-structures.
In addition to their structural roles, the β-helix domains of
the TSP carry an enzymatic activity as endorhamnosidases.
Surprisingly, the active site of Sf6 TSP is located in the cleft
between two subunits of the trimer, whereas in HK620 TSP it
is located within a subunit.
Cancer Research 111