A solution to a hairy problem in forensic science

November 06, 2019

In an effort to make hair comparison a more useful technique for investigating crimes, scientists at the National Institute of Standards and Technology (NIST) have developed a new way to dissolve hair proteins without destroying them. Once in solution, the protein molecules from two hairs can be analyzed and compared, yielding objective, quantitative results.

Hair can be an excellent forensic material because it lasts a long time. Even archaeological sites can yield intact hair. Compare that to DNA, which degrades relatively quickly, especially when exposed to the elements.

But the fact that hair is so durable makes it difficult to work with. Hair is made up of protein fibers, called keratins, that are braided together like wires in a cable. Those protein cables are then braided into still larger cables that are difficult to dissolve without losing the keratin.

But, said Zheng Zhang, a NIST research chemist and co-author of the study, "Our method yields enough keratin for analysis even when starting with a very small amount of hair."

Until now, protocols for dissolving hair keratins required roughly 10 milligrams (mg) of hair, or about 100 5-centimeter (cm) strands -- a quantity not likely to be found at a crime scene. The new method, recently described in the Journal of Forensic Sciences, requires only a single 5-cm strand of hair.

Methods for comparing hair proteins will still need to be validated before they can be used in court, where life and liberty may hang in the balance. But this new method for dissolving hair protein removes a major obstacle.

Forensic scientists have been analyzing hair for decades by visually comparing samples under a microscope. In the past, some experts have testified that hair from a crime scene came from a specific individual. Such claims, which may have led to innocent people being wrongly convicted, are no longer considered scientifically valid. Today, microscopic hair comparison is used in a more limited way, not to identify suspects but to rule them out.

In recent years, forensic scientists have also been analyzing a type of genetic material in hair called mitochondrial DNA. This type of DNA can help in an investigation, but unlike regular DNA, it cannot be used to identify an individual.

However, proteomics -- the study of all the proteins in an organism or part of an organism, in this case, hair -- can be used to identify an individual. Proteins are made up of building blocks called amino acids, which are strung together in a particular sequence, like beads on a string. In hair, those sequences vary slightly from person to person, and because they are coded in our genes, they are permanent features of our identity.

In 2016, researchers at Lawrence Livermore National Laboratory showed that these variations can be used to compare hair proteins with mathematical precision. However, extracting keratin from hair required multiple soakings, grindings and chemical treatments. Because some keratin is lost with each step, a relatively large amount of hair was needed to recover enough of it for analysis.

Through a series of trials, the NIST researchers developed a single-step method that involves heating the hair in a solution with detergent. Because the new process involves only a single step, more protein is recovered from a given amount of hair. Once the keratins are extracted, they can be analyzed using standard methods for proteomic analysis, which involves running them through an instrument called a mass spectrometer.

In addition to developing the new dissolving protocol, the researchers identified 12 new genetically determined variations in human hair. These still need to be verified with genetic studies, but, said NIST research chemist and co-author Meghan Burke, "More points of comparison will mean more precise results."

Going forward, the researchers hope to identify additional variations in hair proteins. They are also working with geneticists at NIST to map keratin variations to the genetic sequences that give rise to them. That will allow comparisons not only of one hair to another, but of a hair to a DNA sample. In other words, if a hair is found at one crime scene and a bloodstain is found at another, investigators might be able to assess whether they came from the same individual.

"Analyzing hair proteins will allow forensic scientists to answer some very important questions that they couldn't answer before," Burke said.
Paper: Z. Zhang, M. Burke, W. Wallace, Y. Liang, S. Sheetlin, Y. Mirokhin, D. Tchekhovskoi, S. Stein. Sensitive Method for the Confident Identification of Genetically Variant Peptides in Human Hair Keratin. Journal of Forensic Sciences. Published online Oct. 31, 2019. DOI: 10.1111/1556-4029.14229

National Institute of Standards and Technology (NIST)

Related DNA Articles from Brightsurf:

A new twist on DNA origami
A team* of scientists from ASU and Shanghai Jiao Tong University (SJTU) led by Hao Yan, ASU's Milton Glick Professor in the School of Molecular Sciences, and director of the ASU Biodesign Institute's Center for Molecular Design and Biomimetics, has just announced the creation of a new type of meta-DNA structures that will open up the fields of optoelectronics (including information storage and encryption) as well as synthetic biology.

Solving a DNA mystery
''A watched pot never boils,'' as the saying goes, but that was not the case for UC Santa Barbara researchers watching a ''pot'' of liquids formed from DNA.

Junk DNA might be really, really useful for biocomputing
When you don't understand how things work, it's not unusual to think of them as just plain old junk.

Designing DNA from scratch: Engineering the functions of micrometer-sized DNA droplets
Scientists at Tokyo Institute of Technology (Tokyo Tech) have constructed ''DNA droplets'' comprising designed DNA nanostructures.

Does DNA in the water tell us how many fish are there?
Researchers have developed a new non-invasive method to count individual fish by measuring the concentration of environmental DNA in the water, which could be applied for quantitative monitoring of aquatic ecosystems.

Zigzag DNA
How the cell organizes DNA into tightly packed chromosomes. Nature publication by Delft University of Technology and EMBL Heidelberg.

Scientists now know what DNA's chaperone looks like
Researchers have discovered the structure of the FACT protein -- a mysterious protein central to the functioning of DNA.

DNA is like everything else: it's not what you have, but how you use it
A new paradigm for reading out genetic information in DNA is described by Dr.

A new spin on DNA
For decades, researchers have chased ways to study biological machines.

From face to DNA: New method aims to improve match between DNA sample and face database
Predicting what someone's face looks like based on a DNA sample remains a hard nut to crack for science.

Read More: DNA News and DNA Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.