THE SCRIPPS
and
RESEARCHINSTITUTE
UCSD'S SCRIPPSINSTITUTION
OF OCEANOGRAPHY
HOLD FORSCIENCEEMBARGO
Broadcast-- 3 p.m., PacificTime, Thursday,December16, 1993
P ri n t-- F ri d a y,D e ce mb er17, 1993
Media Contacts:
Cindy Clark or Janet Howard, ScrippsInstitutionof Oceanography
(619) 534-1294
RobinGoldsmith,The ScrippsResearchInstitute
( 6 1 9 )5 5 4 - 8 1 3 4
SAN DIEGOSCIENTISTSPROVIDENEW
CLUESTO THE BIOCHEMISTRY
OF FERTILIZATION
La Jolla, CA. -- A team of researchersat The ScrippsResearchInstitute
and UCSD's ScrippsInstitutionof Oceanographyhas discoveredthe
molecularstructureof a key proteinthat offers insight into the processof
human fertilizationand reproductionand may lead to the developmentof a
new class of contraceptives.
T he fi n d i n g ,to b e p u b l i shedin the Dec. 17 issueof the jour nal
Science,elucidatesthe structureof the proteinthat allows abalonesperm
to fertilizeeggs.
"The molecularprocessby which animalsperm penetrateegg
envelopesisn't known. The abaloneprovidesa model system in which to
study it," said Victor D. Vacquier,a scientistat UCSD's ScrippsInstitution
of Oceanographywho purifieda fertilizationproteincalled lysin found in
a b a l o n esp e rm.
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Page 2--Abalone
Three researchersat The ScrippsResearchInstitute,Andy Shaw,
Duncan McRee,and David Stout, solvedthe three-dimensional
structureof
abalonelysin using X-ray crystallography.The processinvolvesscanning
crystals of lysin with an X-ray beam and then studyingthe diffraction
pattern, or arrangementof spots the crystal creates on film, to construct a
picture of how the atoms in each moleculeare arranged.
Accordingto David Stout, "This is the first time that a fertilization
protein has been visualized.Now that we have determinedthe structureof
the protein,we can conduct experimentsto understandhow it functions."
Abaloneeggs are similarto human eggs in that they are contained
within an envelope.The abalonesperm penetratesthe envelopeby
releasinglysin. Whereasscientistshad previouslypostulatedthat sperm
passedthrough the envelopeby releasinga.nenzymethat destroyedthe
envelope'sintegrity,the new work shows that lysin is not an enzyme. lt
interactswith the surfaceof the envelope,causingit to disassemble. "The
envelopeis made up of long, thin fibers that are intertwinedin an extremely
tight and tough meshwork,and what the lysin proteindoes is to destroy
t h e c o h esi ve n e ss
o f th e fi b e rs,"Vacquiersaid.
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Page3 --Abalone
The mechanismlysin usesto disruptthe structuralintegrityof the
egg enveloperemainsunclear.lt may act, however, by destroyinghydrogen
bonds or inducingstructuralchangesin envelopemoleculesthat cause
them to dissociate.The fact that the processis non-enzymaticis
significant,Vacquiersaid, becausesimilarinteractionsmay be occurringin
other processeswhere cells try to invadeeach other, includingcancer.
Accordingto the scientists,no one has ever lookedfor surfaceactive
proteinsbeing involvedin normaldevelopmentor diseaseprocesses.
Becauseabalonereleasetheir sperm and eggs into the sea, survival
of the specieshingeson the ability of the sperm and egg to successfully
recognizeand interactwith one another.
The researchersobservedthat lysin appearsto be speciesspecific.
Sperm of red abalone,for example,were found to be much more capableof
penetratingthe envelopesof eggs from red.abalonethan those from the
pinkabalone.
"We think that changesin the structureof lysin might be part of the
speciationprocess,"Vacquiersaid.
Scientistsoften conduct fertilizationresearchusing marine
invertebratesbecausethey can easilyobtain the large quantitiesof eggs
and sperm neededfor study. Much of the work conductedin marine
invertebrateslays the groundworkfor understandingfertilizationin other
a n i m a l s,i n cl u d i n gh u ma n s.