steigbigel_edit.qxp 14/11/07 10:51 Page 14
HIV & AIDS
Figure 1: 3’ Processing and Strand Transfer
second conserved motif, HHCC, binds a Zn
2+
ion, also necessary for activity,
and promotes IN self-association.
2
A third motif, rich in basic amino acids,
INTEGRASE
serves as a putative nuclear localization signal.
3
I
5’
3’
3’ 5’
HIV1 DNA
For technical and other reasons, structural studies of IN were slow to
II
5’
Ö-H
reach fruition, explaining in part why pharmacological inhibitors of
Ö-H
5’
protease and RT preceded those for IN. Now, there is a wealth of
crystallographic and solution-phase information
4,5
showing that IN has
three structural domains roughly corresponding to the locations of DDE,
HHCC, and DNA/protein binding.
IN carries out two quite dissimilar reactions, separate in time and space. The
5’
Ö-H
3’
first, the 3’-processing step, consists of engagement of IN with the long
Ö-H
III
3’
5’
terminal repeat (LTR) of the virus and recognition of a dinucleotide, CpA, at
5’
3’
3’ 5’
which the RT-generated replicon will be cleaved. This cut but blunt-ended
Cellular DNA
IV
strand of DNA is processed further to remove a dinucleotide from each 3’-
5’
5’ OH and, hence, generate ‘sticky ends’ or overhangs in the complementary
strand. Functional studies show active IN as a dimer of two 32kDa subunits.
V
5’
5’
Each subunit engages with a 3’-OH grouping on the exposed ends of the
3’
Integrated proviral DNA
cut dsDNA transposon, and trims it. In certain phases of its activity, IN is
perhaps a ‘dimer of dimers,’ or even a higher-order polymer,
6,7
but the
Figure 2: Raltegravir (MK-0518)
significance of this is as yet unclear.
O O The second step, strand transfer, encompasses activity whereby the dsDNA
replicon is shuttled through the nuclear membrane while bound to IN in a
N N
H
N
pre-integration complex (PIC) with other nucleoproteins. Donor (viral) DNA
F
is held thus in a linear state, keeping the sticky ends apart to prevent circles
N N
forming. The acceptor (host chromosomal) DNA is cut, the viral DNA slides
H
N
into place, and gaps are closed by ligation of both strands, probably by DNA
O
double-strand break repair enzymes that are usually possessed by host cells.
O OH
The steps in both 3’ processing and strand transfer are shown in outline in
Figure 1.
8
Raltegravir/MK-0518
Figure 3a: Percentage of Patients with Virological Response
Figure 3b: Percentage of Patients with Virological Response
<400 copies/ml
<50 copies/ml
BENCHMRK-1 BENCHMRK-2
BENCHMRK-1 BENCHMRK-2
100
100 100
100
80 80
80 80
60 60
60 60
40 40
40 40
rcentage of patients with
Pe
HIV RNA <400 copies/ml
20 20
P
ercentage of patients with
HIV RNA <50 copies/ml
20 20
0 0
0 0
024 8 12 16 24 024 8 12 16 24
024 8 12 16 24 024 8 12 16 24
Weeks
Weeks
Number of contributing patients
Number of contributing patients
Raltegravir* 232 230 158 230 229 128
Raltegravir* 232 230 158 230 229 128
Placebo* 118 118 81 119 119 69
Placebo* 118 118 81 119 119 69
*+OBT p<0.001 at week 16 for both parameters.
*+OBT p<0.001 at week 16 for both parameters.
Non-completer = failure.
Non-completer = failure.
14 US INFECTIOUS DISEASE 2007