StoriescompiledbyR.RamachandranASTRONOMY/MICROBIOLOGY/HEALTH
WHENmedicalemergenciesarise,eitherdue to large-scale
disastersordiseaseoutbreaks,hospitalsandagenciessuchas
the Red Crossare facedwith a severeshortage of donorblood,
especiallydue to the mismatchin bloodtypes.Nowscientists
fromthe Universityof BritishColumbiaclaimthat theyhave
identifiedfromthehumangutenzymesthatcanturntypeAand
B bloodinto O, the universalbloodtype,30 timesmoreeffi-
cientlythanthe previouslystudiedenzymes.Thesefindings
havebeenreportedin “NatureMicrobiology”.
Whenthesefindingswerereportedat the annualmeeting
of the AmericanChemicalSocietyin August2018,one of the
authors,StephenWithers,said:“Wehavebeenparticularly
interestedin enzymesthatallowus to removethe A or B
antigensfromred bloodcells.If you can removethoseanti-
gens,whichare just simplesugars,thenyou can convertA or B
to O blood.”Accordingto him,scientistshavebeenpursuing
this line of researchfor quitesometimebut withoutbeingable
tofind efficientand selectiveenzymesthat are alsosafeand
economicalto do the job.
To assesspotentialenzymecandidatesquickly,Withers
and his collaborator usedmetagenomics.“Withmetagenom-
ics, you takeall of the organismsfroman environmentand
extractthe sumtotalDNAof thoseorganismsall mixedup
together,”Withersexplained.Castingsucha widenet allowed
Withers’teamto samplethe genesof millionsof microorgan-
ismswithoutthe needfor individualcultures.
The researchersthenusedE.colito selectfor DNA-con-
taininggenesthatcodefor enzymesthatcan cleavesugar
residues.So insteadof usingmetagenomics as a meansof
studyingmicrobial ecology,the scientistsusedit to discover
new biocatalysts.
“Thisis a way of get-
ting thatgeneticin-
formationout of the
environment and
intothe laboratory
setting and then
screening for the
activitywe are inter-
ested in,” Withers
said.
Withers’ team sampled DNA from mosquitoes and
leeches,organismsthat degradeblood,but ultimatelyfound
successfulcandidateenzymesin the humangut microbiome
itself.Some of the sugarsof glycosylatedproteinscalled mu-
cinsthatlinethe gut wallare similarin structureto the
antigenson A- and B-typeblood.
The researcherszeroedin on the enzymesthe bacteriause
to pluckthe sugarsoff mucinandfounda newfamilyof
enzymesthatare 30 timesmoreeffectiveat removingred
bloodcell antigensof A- and B-typesthancandidatesthat have
beenreportedearlier.
SCHEMATICof enzymes removing
sugarsfromA- and B-type bloodcells
to make O type,the universalblood.UNIVERSITYOFBRITISHCOLUMBIAEnzymetocreateuniversal
bloodtype
BRYCECARLSONLimitstohumanendurance
RESEARCHERSfromDukeUniversityhavedeterm-
inedthat irrespectiveof the activity,humanenergy
expenditure cannotbe sustainedabove2.5 timesthe
rateof metabolism,or calorieburning,at rest.
CaitlinThurberand colleaguesuseddataon athletes
who competedin globalenduranceevents.Thefind-
ingsare publishedin a recentissueof “Science
Advances”.
The reportsuggeststhat in termsof humanevol-
ution,all humanactivitiessharethe same metabolic
limits, which means naturalselection that enhanced
one endurance ability,suchas running, mayhave
consequentlybenefited manyothers, such as brain
size expansion and gestationlength.
“This defines the realm of what’s possible for
humans,”saidHermanPontzer, a co-author in the
study. Beyondthe ceiling of 2.5 times a person’s
resting metabolic rate, the body starts to break down
its own tissues to make up for the calorie deficit.
The researchersincorporatedoriginaldatafrom
the RaceAcrossthe USA (RAUSA),the longesteventto
datefromwhichmetabolicmeasurementshavebeen
recorded.In this gruellingevent,athletes run from
HuntingtonBeach,California,to Washington,a dis-
tanceof about4,800km, coveringapproximatelya
marathona day, six days a week,for 14-20 weeks.
The researchersfoundthat metabolicratesvar-
ied greatlybasedon the lengthof the endurance
event,withhighmetabolicratesaccompaniedby
decreasesin totalenergyexpenditure.The athletes’
energyexpenditurestartedout relativelyhigh,but
invariablyplungedandflattenedout at 2.5 times
theirbasalmetabolicratefor the remainderof the
event.Thatis to say that the bodycan “downshift”its
metabolismto helpstaywithinsustainable levels.
However,accordingtothestudy,thesamemetabolic
ceilingappliedacrossall events.Energyexpenditure
couldnot be sustainedfor any physicalactivityabove
2.5 timesthe rateof metabolismat rest,meaning
that activitiesinvolvingdifferentmusclegroupsand
organsystemsare all unitedby the sameenergy
intakecontrols.