FT. LAUDERDALE, Fla. _ Two Nobelists _ Sidney Altman andThomas Cech, both protein engineers _ were awarded the MiamiWinter Symposium's distinguished Lynen medals here Sunday. Theyshared the 1989 Nobel prize in chemistry for separately discoveringribozymes _ the catalytic cleavage properties of RNA. Cech is nowat the University of Colorado and Altman is at Yale University.
The awards culminated the first day of the conference, which thisyear focuses on Protein Engineering and Structural Biology. It issponsored by the University of Miami and Bio/Technology. Thisyear's meeting attracted 550 registrants from 25 countries and is thesecond here since it was moved from Miami.
In his acceptance lecture, Cech updated his work on the structure andprotein-cleaving performance of catalytic RNA, which now involvesreplacing not just molecules in nucleic acids, but individual atoms.He then told his audience: "We're now intrigued with . . . the use ofribozymes for possible therapeutic applications. Instead of usingribozymes to try to destroy cellular RNA, we think they can be usedto repair defective RNA molecules."
Cech cited as a generic example of such a pharmaceuticalapplication, "a mutant transcript _ this could be either a nonsensemutation or a missense mutation." He added, "Of course there aremany genetic diseases that are characterized by the transcript stillbeing present, but being defective."
Oral Interferon, Drinkable Insulin Molecules
Closer, perhaps, to pharmaceutical realization was "Oralbioavailability of partially folded proteins," a presentation by SamMilstein, executive vice president and chief scientific officer ofEmisphere Technologies Inc. of Hawthorne, N.Y.
He described how changing the pH (acidity) of alpha-interferon alsoaltered its structural conformation, such that "this protein can beadministered by mouth."
To bend the target protein molecule out of shape, his firmsynthesized small (200 molecular-weight) carrier compounds,specific to alpha-interferon, of which "significant titers showed up inthe systemic circulation of rats" that ingested the solubilized protein.
Dosing the complex into a primate's duodenum by esophagealintubation produced interferon concentrations of 6,000 picogramsper milliliter, "pretty much exactly like what an injection of alpha-interferon would look like," Milstein said.
He added, "This complex was literally rocketed through from thegastrointestinal tract into the systemic circulation, with the protein atfull activity." As a control, when the interferon was thusadministered without its chaperoning carrier compound, "essentiallythere was noise in the [dose response] system; absolutely nothing gotthrough."
Oral insulin, escorted by a carrier molecule specific to that hormone,yielded similar effects.
The compounds bind proteins reversibly, and induce a solubilizingchange in their conformation, from the native to the intermediatestate.
"As of a week ago," Milstein concluded, "Emisphere had screened alibrary of about 800 such protein-specific small carrier molecules"Half a dozen of these are on the company's drawing board, amongothers, human growth hormone and salmon calcitonin. Plus, he said,"we've orally delivered a monoclonal antibody for a vaccine of 2.5million molecular weight."
Milstein later told BioWorld Today that his carrier/proteincomplexes "have been tested in six different mammalian species pluschicks, and we intend to put orally bioavailable growth hormone intohumans this year."
He also mentioned that "a number of major pharmaceuticalcompanies are knocking on Emisphere's door to license these smallmolecules."
From Protein Folding To Signal Transduction
How cells get the message was the name of Monday morning's gamehere.
Structural biologist Heidi Hamm, University of Illinois College ofMedicine in Chicago, took rhodopsin, the retina's visual purple, asher model of how the eye transduces light signals into image. (SeeBioWorld Today, Feb. 6, 1995, p. 1.)
Hamm told BioWorld, "My own finding in today's context ofreceptor specificity was that a particular subclass of G proteins[guanine-nucleoside-binding proteins] interacts with its receptor, andthis is a lead for locking in a conformation of a very importantblocker of receptor interaction.
"The significance of that," Hamm explained, "is that these proteinsare switch proteins. They respond to activated receptors by releasingguanasine diphosphate and triphosphate. And this causes aconformational change that leads to activation of the cell.
"The rhodopsin connection," she continued, "is simply that I havedone a lot of my studies with rhodopsin as a model of guanasineinhibition. It's a very nice model because we can get large amountsof it to study in vitro, whereas very rare receptors for very rarehormones and neurotransmitters we cannot deal with.
"With rhodopsin we've been able to do nuclear transmissionresonance and reconstitutional studies, for example."
She also described the conformational connections to pertussis andcholera: "G proteins are critically involved in the response of cells tohormones. Pertussis and cholera are two species that are known to becaused by a very specific modification of a G protein. In the case ofcholera, GS [stimulatory] causes an unregulated reaction of cyclicAMP in diarrhea.
"In the case of pertussis, it causes a decreased inhibitory interactionwith receptors, and therefore, an increase in cAMP inside the cellthat leads to pertussis.
"In collaboration with Affymax AV [of Amsterdam, TheNetherlands] we studied a random peptide library that had a set ofsequences related to carboxy terminal sequences of guanasineinhibitory alpha. We pulled out higher-affinity analogs to thissequence, that would bind to rhodopsin. We think these could belead compounds for either peptides or non-peptides that could blockreceptor-G protein interaction."
This pharmaceutical potential, Hamm observed, "would not belimited to rhodopsin, but could apply to any of the hundreds ofreceptors that interact with a GI protein."
She concluded: "I would say that what we've been talking about thismorning is the very detailed structural cases of protein-proteininteraction and signal transduction pathways. And I think the futureof biotechnology in this area, which is a very lively area, is to be ableto specifically block these interactions. These are intracellular drugtargets, basically, that promise a lot of specific new tools for eitherstimulating or inhibiting cellular processes." n
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.