Introduction to Forensic Proteomics

The analysis of DNA was a revolutionary practice for Forensic Science. Even cases, cold for decades, got reopened with the hope of finally finding an answer with DNA. But there are things that DNA cannot do. Move aside DNA, forensic scientists are now turning to Proteomics to uncover evidence hidden even from DNA. Allow me to give you a brief introduction to Forensic Proteomics

What is Forensic Proteomics?

Proteomics is the study of the proteome. The Proteome is the collection of proteins that make up a biological organism. Forensic  Proteomics studies the proteins left at a crime scene.

Image 1: Blood Stains at a Crime Scene
Found at https://commons.wikimedia.org/wiki/File:Bloodstains_in_crime_scene_in_1950s_photograph_of_Norway,_from-_Aasted-2_(cropped).jpg

DNA gives you information about which person of interest attended the scene. Proteomics differentiates between the tissue samples. For instance, not only can proteomics differentiate between blood and saliva, but it can also tell the investigator if they are dealing with menstrual blood or blood from a cut (Merkley, 2019). Forensic proteomics focuses on fine details, and these details help an investigator solve a crime.

Is Proteomics a new idea?

I overstated the case when I said ‘move aside DNA’ in my introduction, proteins were studied long before DNA analysis was available. Of course, it was not called proteomics when Mathieu Orfila developed a simple test for blood in 1813. A hundred years later in 1915, scientists developed a test for blood groups, depending on the ABO proteins (History). Other more recent experiments have created the presumptive test for saliva, which detects the protein α-Amylase (Noureddine, 2011). A different test for semen looks for acid phosphatase (Rackley Olsen, 2011). If you would like to learn more about presumptive testing check out ‘What Stain is This?’

These presumptive tests can give false positives and negatives, which is why they remain ‘presumptive’. However, with the latest up-to-date methods, proteomics can confirm these initial tests.

How does Forensic Proteomics work?

Modern methods of proteomics involve Mass Spectrometry, not wet chemistry with its color-changing tests. Previously, finding a protein involved searching for a specific molecule, a method utilized in the presumptive tests mentioned above. If you know what you want to find, then it is easy to design an anti-body to pick it out. This is how the rapid test kits for pregnancy and CoVid 19 work. However, what happens when you are not sure what you are looking for? This is where Mass Spectrometry (MS) comes in.

Mass Spectrometry in Forensic Proteomics

With MS, a scientist studies all the proteins at the same time. To allow MS analysis, the folded protein is denatured, allowing the molecule to flop open. A protein is made up of amino acids. Using enzymes, they chop the larger protein into its constituent amino acid peptides.

Image 2: How Proteomics works
Credit: Biorender.com
Found at https://commons.wikimedia.org/wiki/File:Quantitative_Proteomics.png

MS allows scientists to map out the numbers of each peptide. With this information, they identify the proteins from the original sample. As each tissue and organ has its own variety of proteins, it is possible to work out where the sample originated (Orton, 2020). This specificity tells an investigator if an individual just walked through a crime scene or whether they were in some way involved in the action.

How does proteomics compare with DNA analysis?

When comparing DNA analysis to Proteomics it is vital to remember one key thing, DNA gives the orders and proteins do the work (Merkley, 2019).

Hair at a crime scene

Firstly, let us consider hair, a common fiber found on a crime scene. If the investigators are lucky, a root ball is attached to the hair, from which DNA can be extracted. Most of the time, a hair has no DNA present, or the DNA has degraded. What hair does have is the robust protein, Keratin. Creating Keratin to form hair can destroy DNA. However, DNA orders the hair to be curly or straight, Brunette or Blonde. The links and bonds in Keratin reveal the DNA that ordered its creation (Moore, 2022). Hair is not the only frequent evidence found on a crime scene

Bones at a crime scene

Another regular finding at a crime scene is bones.

Image 3: Bones on a Beach
Found at https://commons.wikimedia.org/wiki/File:Bone_found_on_Shirahamachuo_beach.jpg

Bones protect DNA, making identification easier. However, bare bones give the investigator very little clue as to how long the individual was left in place. As time passes, the proteins in the bone structure undergo deamination, where they lose amino acid groups. How far the deamination process has advanced can give the investigator an idea as to the Time from Death. This is a vital tool in solving historical crime (Moore, 2022).

Both DNA analysis and Proteomics work together to give an investigator the information necessary to solve a crime.

Do the Courts Recognize Forensic Proteomics as Evidence?

In the USA, the evidence must achieve the Daubert Standard to be recognized as evidence. This requires five levels of acceptance (Legal Information Institute, 2022).

1. Has the methodology been tested?
2. Has there been a publication and peer review of the methodology?
3. What is the error rate of the methodology?
4. Are there standards in place to validate the methodology?
5. Has the wider scientific community accepted the methodology?

DNA is well accepted in Courts of Law, because of the statistical basis of the technique. While Proteomics has received peer review in publication, at present the statistics for Forensic Proteomics is in its infancy. The databases required for statistical analysis are still being built. So at present, acceptance in a Court of Law is still on a case-by-case basis (Orton, 2020).

Non-forensic applications of Proteomics

While the case for applications of forensic Proteomics is still in the early stages, the modern version of Proteomics allows the non-forensic implementations of Proteomics. In medicine, proteomics is used to identify tumor markers, enabling doctors to discover if cancer is undergoing metastasis. In other areas, Proteomics reveals some of the hormone doping in Sports. Archaeology also relies on proteomics to unravel the proteins in paints and pottery (Merkley, 2019). Even without forensic applications, proteomics is an up-and-coming area for scientific study.

Conclusion

This brief overview was only an introduction to forensic proteomics. The new scientific methods are rapidly gaining acceptance in medicine and other areas of study. We can hope to see that the many valid processes in which Proteomics can help scientists and researchers will soon be available to help solve crime.

References

Merkley, E.D., (2019). Introduction to Forensic Proteomics. ACS Symposium Series: American Chemical Society. https://pubs.acs.org/doi/pdf/10.1021/bk-2019-1339.ch001

History of Forensics. Alibi Channel. https://alibi.uktv.co.uk/article/history-forensics/#:~:text=Modern%20toxicology%20began%20in%201813,used%20immediately%20in%20criminal%20investigations

Noureddine, M. (2011). Forensic Tests for Saliva: What You Should Know. Forensic Resources: Office of Indigent Defense Services. Aug 15. https://forensicresources.org/2011/forensic-tests-for-saliva-what-you-should-know/

Rackley Olsen, S. (2011). Forensic Tests for Semen: What You Should Know. Forensic Resources. https://ncforensics.wordpress.com/2011/10/19/forensic-tests-for-semen-what-you-should-know/

Orton, R. (2020). Forensic Proteomics: Beyond DNA Profiling. Pacific Northwest National Laboratory. Jan 21. https://www.pnnl.gov/news-media/forensic-proteomics-beyond-dna-profiling

Moore, S. (2022). What is Forensic Proteomics? AZO Life Sciences. Jun 1 https://www.azolifesciences.com/article/What-is-Forensic-Proteomics.aspx

Legal Information Institute. (2022). Daubert Standard. Cornell Law School. https://www.law.cornell.edu/wex/daubert_standard#:~:text=The%20Daubert%20standard%20is%20the,to%20the%20facts%20at%20issue