Award: OCE-1458017

This project was to try and relate ?traditional? approaches in marine organic geochemistry to new ?omic? approaches. The scientific questions we ask today are based on the tools and approaches of the past, but the new types of information being produced can be hard to relate back to the information gained using traditional tools. Proteomics is a good example of this; the new tools allow chemical oceanographers to evaluate strings of amino acids (peptides) but the old tools required that we separate them into individual molecules before analysis. This sets up a dichotomy between new data and old data; none of the results are directly comparable. To further complicate things, the traditional approaches focused on how proteins were being degraded in the ocean (cycling) where the new proteomic tools target the source (organism) and function (in the cell) of the protein and provide no information about protein once it is part of the detritus. To help meld the new and established tools together, we studied a set of samples using both modern proteomics and traditional analyses, and also developed a new proteomic tool that helps bridge the gap between past studies and future evaluations of organic carbon cycling in the ocean. We found that the modern approach of de novo sequencing, where a person does not need to know potential peptide sequences prior to looking for them, can be used to link the degradation history of a protein to its source (type of organisms) and function (what it does in a cell). This is because de novo sequencing can identify peptides when they are partially degraded. Using the comparisons and the new de novo sequencing tools, we discovered some interesting things. The sinking detritus in the equatorial Pacific Ocean contains degraded peptides from autotrophic organisms and those peptides are usually associated with cell membranes. These two things had been hypothesized using older techniques but could not previously be proven. Our new tool allows evaluation of degraded peptides were previously ?invisible? using older or even more modern database-driven proteomic techniques. Thus, for the first time we bridge the gap between geochemical cycling and biological processing of proteins, and can follow a ?molecular protein fossil? into the deep sea and potentially into the geologic record. Similarly, in sediment samples from the Gulf of Maine we saw striking similarities between de novo sequenced peptide fragments (new approach) and traditional measurements (e.g. the ?degradation? state of a sample measured by evaluating compositions of amino acids and looking for specific types of amino acids known to be associated with the degradation process). This is exciting because it allows us to interpret new data based on a known relationship with a large amount of data collected using the ?traditional? approach over the past 40+ years. Last Modified: 08/29/2019 Submitted by: Richard G Keil