{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/130090"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/130090","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Characterization and spatial mapping of isomerized residues in neuropeptides","abstract":"Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2027-08-01","abstract_html":"Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2027-08-01","abstract_has_math":false,"creators":["Okyem, Samuel"],"institution":"University of Illinois Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Chemistry","degree_department":null,"school":null,"contributors":["Sweedler, Jonathan V.","Sweedler, Jonathan V","Gillette, Martha","Shen, Mei","Romanova, Elena V."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-07-10","date_published":"2025-07-10","updated_at":"2026-07-22T22:25:06Z","subjects":["Neuropeptides","Isomers","Mass Spectrometry","Galanin","Isoaspartate"],"languages":["en","eng"],"rights":["Copyright 2025 Samuel Okyem"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/130090","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Sweedler, Jonathan V.","Sweedler, Jonathan V","Gillette, Martha","Shen, Mei","Romanova, Elena V."]},{"key":"dc:creator","label":"Author","values":["Okyem, Samuel"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2025-07-10","2025-08"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Chemistry"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Neuropeptides","Isomers","Mass Spectrometry","Galanin","Isoaspartate"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en","eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2025 Samuel Okyem"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/130090"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2027-08-01","The student, Samuel Okyem, accepted the attached license on 2025-07-08 at 16:59.","The student, Samuel Okyem, submitted this Dissertation for approval on 2025-07-08 at 17:06.","This Dissertation was approved for publication on 2025-07-10 at 10:30.","DSpace SAF Submission Ingestion Package generated from Vireo submission #22447 on 2025-10-25 at 15:30:54","The discovery and characterization of post-translational modifications (PTMs) in neuroendocrine peptides, particularly those that result in peptide diastereomers and positional isomers, such as D-amino acid incorporation, isoaspartate (isoAsp) formation, and differential covalent modifications, remain significantly limited by the lack of comprehensive analytical and -computational methodologies. Neuroendocrine peptides regulate a wide range of physiological processes, including neuromodulation, energy balance, and homeostasis. Consequently, even subtle chemical alterations can profoundly impact their stability, bioavailability, and function. For instance, the presence of D-amino acid residues is known to enhance peptide stability and receptor potency. At the same time, the formation of isoAsp has been associated with increased fibrillization, potentially facilitating peptide storage or contributing to cytotoxicity. To advance our understanding of these structural variants, often referred to as “zero-Dalton” modifications due to their mass equivalence, it is essential to develop robust tools for their detection and characterization. This dissertation presents a comprehensive suite of bioanalytical, computational, and biochemical techniques for the untargeted discovery and site-specific characterization of D-amino acid- and IsoAsp-containing neuropeptides. Additionally, a mass spectrometry imaging (MSI) method based on matrix-assisted laser desorption/ionization trapped ion mobility spectrometry (MALDI-TIMS-MSI) is introduced, enabling spatial mapping of neuropeptides and their isomers at single-cell resolution. Application of these integrated methods led to the discovery of IsoAsp-containing forms in multiple hypothalamic peptides from rat brain, including galanin, and peptides derived from proenkephalin, melanin-concentrating hormone, secretogranin, and pituitary adenylate cyclase-activating peptide (PACAP) prohormones. Furthermore, three novel D-amino acid-containing peptides were identified from the nervous system of A. californica. These methods also enabled the identification and structural characterization of diacetylated and triacetylated forms of α-melanocyte-stimulating hormone (α-MSH) in both rat and human pituitary tissue. These acetylation variants were found to exhibit species-specific patterns and region-specific localization, offering new insights into their potential physiological roles. The work presented in this dissertation advances the field of peptidomics by providing comprehensive tools for probing subtle yet functionally important modifications."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Characterization and spatial mapping of isomerized residues in neuropeptides"]}]}],"canonical_facts":{"dc:contributor":["Sweedler, Jonathan V.","Sweedler, Jonathan V","Gillette, Martha","Shen, Mei","Romanova, Elena V."],"dc:creator":["Okyem, Samuel"],"dc:date":["2025-07-10","2025-08"],"dc:description":["Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2027-08-01","The student, Samuel Okyem, accepted the attached license on 2025-07-08 at 16:59.","The student, Samuel Okyem, submitted this Dissertation for approval on 2025-07-08 at 17:06.","This Dissertation was approved for publication on 2025-07-10 at 10:30.","DSpace SAF Submission Ingestion Package generated from Vireo submission #22447 on 2025-10-25 at 15:30:54","The discovery and characterization of post-translational modifications (PTMs) in neuroendocrine peptides, particularly those that result in peptide diastereomers and positional isomers, such as D-amino acid incorporation, isoaspartate (isoAsp) formation, and differential covalent modifications, remain significantly limited by the lack of comprehensive analytical and -computational methodologies. Neuroendocrine peptides regulate a wide range of physiological processes, including neuromodulation, energy balance, and homeostasis. Consequently, even subtle chemical alterations can profoundly impact their stability, bioavailability, and function. For instance, the presence of D-amino acid residues is known to enhance peptide stability and receptor potency. At the same time, the formation of isoAsp has been associated with increased fibrillization, potentially facilitating peptide storage or contributing to cytotoxicity. To advance our understanding of these structural variants, often referred to as “zero-Dalton” modifications due to their mass equivalence, it is essential to develop robust tools for their detection and characterization. This dissertation presents a comprehensive suite of bioanalytical, computational, and biochemical techniques for the untargeted discovery and site-specific characterization of D-amino acid- and IsoAsp-containing neuropeptides. Additionally, a mass spectrometry imaging (MSI) method based on matrix-assisted laser desorption/ionization trapped ion mobility spectrometry (MALDI-TIMS-MSI) is introduced, enabling spatial mapping of neuropeptides and their isomers at single-cell resolution. Application of these integrated methods led to the discovery of IsoAsp-containing forms in multiple hypothalamic peptides from rat brain, including galanin, and peptides derived from proenkephalin, melanin-concentrating hormone, secretogranin, and pituitary adenylate cyclase-activating peptide (PACAP) prohormones. Furthermore, three novel D-amino acid-containing peptides were identified from the nervous system of A. californica. These methods also enabled the identification and structural characterization of diacetylated and triacetylated forms of α-melanocyte-stimulating hormone (α-MSH) in both rat and human pituitary tissue. These acetylation variants were found to exhibit species-specific patterns and region-specific localization, offering new insights into their potential physiological roles. The work presented in this dissertation advances the field of peptidomics by providing comprehensive tools for probing subtle yet functionally important modifications."],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/130090"],"dc:language":["en","eng"],"dc:rights":["Copyright 2025 Samuel Okyem"],"dc:subject":["Neuropeptides","Isomers","Mass Spectrometry","Galanin","Isoaspartate"],"dc:title":["Characterization and spatial mapping of isomerized residues in neuropeptides"],"dc:type":["text"],"thesis:degree_discipline":["Chemistry"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:06Z"}