View source for Hemoglycin

{{Short description|Space polymer claimed to be of extraterrestrial origin}}
{{Use dmy dates|date=January 2023}}
{{Infobox heteropolypeptide
 | heteropolymer = Hemoglycin
 | polymer_type = [[Glycine]]-containing [[space polymer]] of [[amino acid]]s found in [[meteorite]]s
 | protein_fufyfd = 
 | function = unknown, although possibly able to split water to [[hydroxyl]] and [[hydrogen]] moieties<ref name="ARX-20200222" />
 | cofactors = 
 | image = File:Allende meteorite slice ASU.jpg
 | image_source = Hemoglycin was found in Acfer 086, an [[Allende meteorite]] similar to that pictured.
}}

'''Hemoglycin''' (previously termed [[hemolithin]]) is a [[space polymer]] that is the first [[polymer]] of [[amino acid]]s found in [[meteorite]]s.<ref name="MPS-2015">{{cite journal|last1=McGeoch|first1=J.E.M.|last2=McGeoch|first2=M.W.|date=2015|title=Polymer amide in the Allende and Murchison meteorites.|journal=[[Meteoritics & Planetary Science]]|volume=50|pages=1971–1983|bibcode=2015M&PS...50.1971M|doi=10.1111/maps.12558|number=12|s2cid=97089690|doi-access=free}}</ref><ref name="SR-20220928">{{cite journal |last1=McGeogh |first1=Julie E. M. |last2=McGeogh |first2=Malcolm W. |title=Chiral 480nm absorption in the hemoglycin space polymer: a possible link to replication |date=28 September 2022 |journal=[[Scientific Reports]] |volume=12 |issue=1 |page=16198 |doi=10.1038/s41598-022-21043-4 |pmid=36171277 |pmc=9519966 }}</ref><ref name="SD-20210629">{{cite news |author=Staff |title=Polymers in meteorites provide clues to early solar system |url=https://www.sciencedaily.com/releases/2021/06/210629120835.htm |date=29 June 2021 |work=[[Science Digest]] |accessdate=9 January 2023 }}</ref>

== Structure ==
Structural work has determined that its 1,494 [[Dalton (unit)|Dalton]] core unit ([[Glycine]]<sub>18</sub> / [[Glycine|Hydroxy-glycine]]<sub>4</sub> / [[Iron oxide|Fe<sub>2</sub>O<sub>4</sub>]]) contains [[iron]], but not [[lithium]], leading to the more general term hemoglycin for these molecules.<ref name="ARX-20200222">{{cite arXiv |last1=McGeoch |first1=Malcolm. W. |last2=Dikler |first2=Sergei |last3=McGeoch |first3=Julie E. M. |title=Hemolithin: a Meteoritic Protein containing Iron and Lithium |date=22 February 2020 |eprint=2002.11688 |class=astro-ph.EP }}</ref><ref name="ARX-20210221">{{cite arXiv |last1=McGeoch |first1=M. W. |last2=Dikler |first2=S. |last3=McGeoch |first3=J.E.M. |title=Meteoritic Proteins with Glycine, Iron and Lithium |date=21 February 2021 |eprint=2102.10700 |class=physics.chem-ph }}</ref> The hemoglycin core contains a total of 22 glycine residues in an [[Antiparallel (biochemistry)|anti-parallel beta sheet chain]] that is terminated at each end by an iron atom plus two [[oxygen]]s. Four of these glycine residues are oxidized to hydroxy-glycine with hydroxy groups (-OH) on the alpha carbon. This structure was determined by [[mass spectrometry]] of meteoritic solvent extracts<ref name="ARX-20200222" /><ref name="MPS-2015" /><ref name="ARX-20210221" /> and has been confirmed in [[X-ray scattering]] by crystals of hemoglycin,<ref name="PF-20210629">{{cite journal |last1=McGeoch |first1=Julie E. M. |last2=McGeoch |first2=Malcolm W. |title=Structural Organization of Space Polymers |date=29 June 2021 |journal=[[Physics of Fluids]] |volume=33 |issue=6 |doi=10.1063/5.0053302 |s2cid=236281487 |doi-access=free }}</ref> and also by [[optical absorption]].<ref name="SR-20220928" /> Crystals show a 480&nbsp;nm characteristic absorption that can only exist when hydroxy-glycine residues have R [[chirality]] and are C-terminal bonded to iron.<ref name="PF-20210629" />

== History ==
Because hemoglycin has now been found to be the dominant polymer of amino acids in 6 different [[meteorite]]s ([[Allende meteorite|Allende]],<ref name="ASMP-2022">{{cite journal |last=Jujeczko |first=Pawel |title=Lessons learned from the examinations of Allende meteorite |url=http://psjd.icm.edu.pl/psjd/element/bwmeta1.element.psjd-fba8e9c5-7d12-444b-831b-c720769fcfc8/c/ASMP-Roczniki-vol13-Jujeczko1.pdf |date=2022 |journal=Acta Societatis Metheoriticae Polonorium |volume=13 |pages=37–46 |accessdate=10 January 2023 }}</ref> [[January–March 2020 in science#February|Acfer 086]], [[:File:Pb-Pb dating of meteorites.jpg|Efremovka]], [[Carbonaceous chondrite#CV group|Kaba]], [[Orgueil (meteorite)|Orgueil]] and [[Sutter's Mill meteorite|Sutter's Mill]]), each time with the same structure, it has been proposed<ref name="SR-20220928" /><ref name="PF-20210629" /> that it is produced by a process of [[template replication]]. The measured 480&nbsp;nm absorbance is larger than expected for a [[Racemization|racemic distribution]] of R and S chirality in the hydroxy-glycine residues, indicating an R chirality excess in the polymer. Modeling of template replication that is assumed to depend on 480&nbsp;nm absorption leads to an excess of R chirality and thus is consistent with this finding.

== Significance ==
Hemoglycin is a completely [[Abiotic component|abiotic molecule]] that forms in [[molecular cloud]]s which go on to become [[protoplanetary disk]]s, long before biochemistry on [[exoplanet]]s like Earth begins. Hemoglycin via its glycine could seed an exoplanet (one able to support early biochemistry), but its main function appears to be the [[Accretion (astrophysics)|accretion of matter]] via formation of an extensive [[Sphere packing|low-density lattice]]<ref name="PF-20210629" /> in space in a protoplanetary disk. Besides being present in carbonaceous meteorites, hemoglycin has also been extracted and crystallized from a fossil [[stromatolite]] that formed on Earth 2.1 billion years ago.<ref>{{Cite arXiv |eprint=2309.17195 |class=physics.geo-ph |title=Fossil and present-day stromatolite ooids contain a meteoritic polymer of glycine and iron |last1=McGeoch |first1=Julie E. M. |first2=A. J. |last2=Frommelt |first3=R. L. |last3=Owen |last4=Cinque |first4=Gianfelice |last5=McClelland |first5=Arthur |last6=Lageson |first6=David |first7=M. W. |last7=McGeoch |date=2023 }}</ref> Potentially this fossil hemoglycin was delivered to Earth during the [[Late Heavy Bombardment]] (LHB). Data to support this is that the hemoglycin in the fossil has extraterrestrial isotopes similar to that in meteorites.

The polymer on the [[Precambrian|precambrian Earth]] could have driven the [[Great Oxygenation Event]] (GOE) beginning 2.4 Gya by splitting water in response to [[ultraviolet]] irradiation. Also, it could have provided an energy source to early biochemistry and/or it could have simply delivered a source of [[Glycine|polymer glycine]].

==See also==
{{div col|colwidth=30em}}
* [[Ancient protein]]
* [[Bubble (physics)]]
* [[Earliest known life forms]]
* [[Evolutionary history of life]]
* [[Extraterrestrial: The First Sign of Intelligent Life Beyond Earth]]
* [[List of interstellar and circumstellar molecules]]
* [[Panspermia]]
* [[Protein]]
{{div col end}}

==References==
{{reflist|colwidth=30em}}

{{Origin of life}}
{{Iron compounds}}
{{Extraterrestrial life}}
{{Molecules detected in outer space}}
{{portal bar|Astronomy|Biology|Chemistry|Evolutionary biology|Outer space}}

[[Category:Astrobiology]]
[[Category:Biological hypotheses]]
[[Category:Iron compounds]]
[[Category:Origin of life]]
[[Category:Panspermia]]
[[Category:Prebiotic chemistry]]
[[Category:Proteins]]