DNA profiling is often used for identification in crime scene investigations and in archaeological digs because DNA is unique to each individual. However, environmental and chemical processes can degrade DNA, limiting its usefulness over time.
Protein, on the other hand, is more stable than DNA but can also have variations that may be unique to the individual. In a recently published study, Glendon Parker, a biochemist from the Lawrence Livermore National Laboratory, and his team investigated whether proteins found in human hair could offer a new identification tool.
The researchers examined hair samples from six deceased individuals who died up to 250 years ago, demonstrating the robustness of hair proteins. They then began analyzing these samples along with hair samples from 76 living people of European American and African descent. To date, this analysis has revealed a total of 185 hair protein markers, which the researchers estimate would be sufficient to provide a unique pattern that could distinguish one person among a population of 1 million.
The authors hope to identify a core set of about 100 protein markers that would be sufficient to distinguish an individual among the entire world’s population using a single hair. Parker says, “This project has the potential to have a social and legal impact as well as a purely scientific one.”
To learn more about Parker’s research and its broader impact, I interviewed him via email.
How did you become interested in studying unique protein markers in hair? What prompted you to investigate protein as an identifier?
G: I was preparing a grant and needed to come up with another research project to increase the impact of the proposal. A colleague proposed looking at a splice variation in a hair shaft protein using antibodies. I realized that single amino acid changes were a much better target to go after. Peptides with these variants can be detected using proteomic methods and be used to predict the composition of someone’s DNA.
While you were conducting your study did you find anything that surprised you?
GP: Yes. I was surprised that we found genetically variant peptides in archaeological hair, even hair that was highly degraded.
Were there any limitations to your study?
GP: As with any technology there are several. Our markers are less discriminating than the markers currently used in DNA-typing. We therefore need more of them. The population of proteins that can be detected in any tissue also limits us; unlike DNA typing, we do not have the whole genome to work with and are limited to the protein population in the biological evidence.
How does this study help improve our understanding of how human beings may be identified?
GP: Protein-based identification expands the tool set that investigators can bring to a crime scene or archaeological site. We can ask new questions and get more information from available material, such as hair shafts that are currently underutilized. It means that we need to think more broadly, and biologically, about forensic evidence.
What are the next steps for your research on this new identification technique?
GP: For this to be used as a forensic tool, we need to accomplish two things: we need to reduce sample size to a single hair, and we need to nail down the biostatistics and determine the best way to apply the product-rule. We are having good success with both of these goals. We also need to expand our pool of genetically variant peptides. Better instrumentation and improvements in sample preparation and bioinformatics workflows mean that we can now consistently achieve powers of discrimination over 1 in 100,000, and sometimes 1 in a million.
Research Article: Parker GJ, Leppert T, Anex DS, Hilmer JK, Matsunami N, Baird L, et al. (2016) Demonstration of Protein-Based Human Identification Using the Hair Shaft Proteome. PLoS ONE 11(9): e0160653. doi:10.1371/journal.pone.0160653
Image Credit: Julie Russell/LLNL