Amazing Pokeweed
Blee811@aol.com (Mon, 15 Aug 2005 07:24:01 PDT)

In a message dated 8/14/2005 10:55:18 P.M. Eastern Standard Time,
jorna@mobilixnet.dk writes:

viruses

===>I didn't know this and Alberto's posting prompted me to look a little
further into pokeweed. I found one abstract, quoted below, that indicates
pokeweed may also be helpful in HIV cases. It appears to be a most complex plant.

Bill Lee

The Biotherapy and Drug Discovery Program, Parker Hughes Cancer Center, 2699
Patton Road, St. Paul, MN 55113, USA.

Pokeweed antiviral protein III (PAP-III), a naturally occurring protein
isolated from late summer leaves of the pokeweed plant (Phytolacca americana),
has potent anti-HIV activity by an as yet undetermined molecular mechanism.
PAP-III belongs to a family of ribosome-inactivating proteins that catalytically
deadenylate ribosomal and viral RNA. The chemical modification of PAP-III by
reductive methylation of its lysine residues significantly improved the
crystal quality for X-ray diffraction studies. Trigonal crystals of the modified
PAP-III, with unit cell parameters a=b=80.47A, c=76.21A, were obtained using
30% PEG400 as the precipitant. These crystals contained one enzyme molecule
per asymmetric unit and diffracted up to 1.5A, when exposed to a synchrotron
source. Here we report the X-ray crystal structure of PAP-III at 1.6A
resolution, which was solved by molecular replacement using the homology model of
PAP-III as a search model. The fold typical of other ribosome-inactivating
proteins is conserved, despite several differences on the surface and in the loop
regions. Residues Tyr(69), Tyr(117), Glu(172), and Arg(175) are expected to
define the active site of PAP-III. Molecular modeling studies of the
interactions of PAP-III and PAP-I with a single-stranded RNA heptamer predicted a more
potent anti-HIV activity for PAP-III due to its unique surface topology and
more favorable charge distribution in its 20A-long RNA binding active center
cleft. In accordance with the predictions of the modeling studies, PAP-III
was more potent than PAP-I in depurinating HIV-1 RNA.