Distinct Differences in Structural States of Conserved Histidines in Two Related Proteins

NMR Studies of the Chemokines CXCL1 and CXCL8 in the Free Form and Macromolecular Complexes

Krishna Mohan Sepuru, Krishna Rajarathnam

Research output: Contribution to journalArticle

Abstract

Hydrogen-bonding and ionic interactions play fundamental roles in macromolecular recognition and function. In contrast to lysines and arginines, how histidines mediate these interactions is less well-understood due to the unique properties of its side chain imidazole that include an aromatic ring with two titratable nitrogens, a pKa that can vary significantly, and the ability to exist in three distinct forms: protonated imidazolium and two tautomeric neutral (Nδ1 and Nϵ2) states. Here, we characterized the structural features of histidines in the chemokines CXCL8 and CXCL1 in the free, GAG heparin-bound, and CXCR2 receptor N-terminal domain-bound states using solution NMR spectroscopy. CXCL8 and CXCL1 share two conserved histidines, one in the N-loop and the other in the 30s loop. In CXCL8, both histidines exist in the Nϵ2 tautomeric state in the free, GAG-bound, and receptor-bound forms. On the other hand, in unliganded CXCL1, each of the two histidines exists in two states, as the neutral Nϵ2 tautomer and charged imidazolium. Further, both histidines exclusively exist as the imidazolium in the GAG-bound and as the Nϵ2 tautomer in the receptor-bound forms. The N-loop histidine alone in both chemokines is involved in direct GAG and receptor interactions, indicating the role of the 30s loop varies between the chemokines. Our observation that the structural features of conserved histidines and their functional role in two related proteins can be quite different is novel. We further propose that directly probing the imidazole structural features is essential to fully appreciate the molecular basis of histidine function.

Original languageEnglish (US)
Pages (from-to)5969-5977
Number of pages9
JournalBiochemistry
Volume57
Issue number41
DOIs
StatePublished - Oct 16 2018

Fingerprint

Chemokine CXCL1
Macromolecular Substances
Interleukin-8
Histidine
Nuclear magnetic resonance
Proteins
Chemokines
Interleukin-8B Receptors
Hydrogen Bonding
Nuclear magnetic resonance spectroscopy
Lysine
Arginine
Heparin
Hydrogen bonds
Magnetic Resonance Spectroscopy
Nitrogen

ASJC Scopus subject areas

  • Biochemistry

Cite this

@article{75f15bc475d742f5b7fb4c85698048bb,
title = "Distinct Differences in Structural States of Conserved Histidines in Two Related Proteins: NMR Studies of the Chemokines CXCL1 and CXCL8 in the Free Form and Macromolecular Complexes",
abstract = "Hydrogen-bonding and ionic interactions play fundamental roles in macromolecular recognition and function. In contrast to lysines and arginines, how histidines mediate these interactions is less well-understood due to the unique properties of its side chain imidazole that include an aromatic ring with two titratable nitrogens, a pKa that can vary significantly, and the ability to exist in three distinct forms: protonated imidazolium and two tautomeric neutral (Nδ1 and Nϵ2) states. Here, we characterized the structural features of histidines in the chemokines CXCL8 and CXCL1 in the free, GAG heparin-bound, and CXCR2 receptor N-terminal domain-bound states using solution NMR spectroscopy. CXCL8 and CXCL1 share two conserved histidines, one in the N-loop and the other in the 30s loop. In CXCL8, both histidines exist in the Nϵ2 tautomeric state in the free, GAG-bound, and receptor-bound forms. On the other hand, in unliganded CXCL1, each of the two histidines exists in two states, as the neutral Nϵ2 tautomer and charged imidazolium. Further, both histidines exclusively exist as the imidazolium in the GAG-bound and as the Nϵ2 tautomer in the receptor-bound forms. The N-loop histidine alone in both chemokines is involved in direct GAG and receptor interactions, indicating the role of the 30s loop varies between the chemokines. Our observation that the structural features of conserved histidines and their functional role in two related proteins can be quite different is novel. We further propose that directly probing the imidazole structural features is essential to fully appreciate the molecular basis of histidine function.",
author = "Sepuru, {Krishna Mohan} and Krishna Rajarathnam",
year = "2018",
month = "10",
day = "16",
doi = "10.1021/acs.biochem.8b00756",
language = "English (US)",
volume = "57",
pages = "5969--5977",
journal = "Biochemistry",
issn = "0006-2960",
publisher = "American Chemical Society",
number = "41",

}

TY - JOUR

T1 - Distinct Differences in Structural States of Conserved Histidines in Two Related Proteins

T2 - NMR Studies of the Chemokines CXCL1 and CXCL8 in the Free Form and Macromolecular Complexes

AU - Sepuru, Krishna Mohan

AU - Rajarathnam, Krishna

PY - 2018/10/16

Y1 - 2018/10/16

N2 - Hydrogen-bonding and ionic interactions play fundamental roles in macromolecular recognition and function. In contrast to lysines and arginines, how histidines mediate these interactions is less well-understood due to the unique properties of its side chain imidazole that include an aromatic ring with two titratable nitrogens, a pKa that can vary significantly, and the ability to exist in three distinct forms: protonated imidazolium and two tautomeric neutral (Nδ1 and Nϵ2) states. Here, we characterized the structural features of histidines in the chemokines CXCL8 and CXCL1 in the free, GAG heparin-bound, and CXCR2 receptor N-terminal domain-bound states using solution NMR spectroscopy. CXCL8 and CXCL1 share two conserved histidines, one in the N-loop and the other in the 30s loop. In CXCL8, both histidines exist in the Nϵ2 tautomeric state in the free, GAG-bound, and receptor-bound forms. On the other hand, in unliganded CXCL1, each of the two histidines exists in two states, as the neutral Nϵ2 tautomer and charged imidazolium. Further, both histidines exclusively exist as the imidazolium in the GAG-bound and as the Nϵ2 tautomer in the receptor-bound forms. The N-loop histidine alone in both chemokines is involved in direct GAG and receptor interactions, indicating the role of the 30s loop varies between the chemokines. Our observation that the structural features of conserved histidines and their functional role in two related proteins can be quite different is novel. We further propose that directly probing the imidazole structural features is essential to fully appreciate the molecular basis of histidine function.

AB - Hydrogen-bonding and ionic interactions play fundamental roles in macromolecular recognition and function. In contrast to lysines and arginines, how histidines mediate these interactions is less well-understood due to the unique properties of its side chain imidazole that include an aromatic ring with two titratable nitrogens, a pKa that can vary significantly, and the ability to exist in three distinct forms: protonated imidazolium and two tautomeric neutral (Nδ1 and Nϵ2) states. Here, we characterized the structural features of histidines in the chemokines CXCL8 and CXCL1 in the free, GAG heparin-bound, and CXCR2 receptor N-terminal domain-bound states using solution NMR spectroscopy. CXCL8 and CXCL1 share two conserved histidines, one in the N-loop and the other in the 30s loop. In CXCL8, both histidines exist in the Nϵ2 tautomeric state in the free, GAG-bound, and receptor-bound forms. On the other hand, in unliganded CXCL1, each of the two histidines exists in two states, as the neutral Nϵ2 tautomer and charged imidazolium. Further, both histidines exclusively exist as the imidazolium in the GAG-bound and as the Nϵ2 tautomer in the receptor-bound forms. The N-loop histidine alone in both chemokines is involved in direct GAG and receptor interactions, indicating the role of the 30s loop varies between the chemokines. Our observation that the structural features of conserved histidines and their functional role in two related proteins can be quite different is novel. We further propose that directly probing the imidazole structural features is essential to fully appreciate the molecular basis of histidine function.

UR - http://www.scopus.com/inward/record.url?scp=85054384699&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85054384699&partnerID=8YFLogxK

U2 - 10.1021/acs.biochem.8b00756

DO - 10.1021/acs.biochem.8b00756

M3 - Article

VL - 57

SP - 5969

EP - 5977

JO - Biochemistry

JF - Biochemistry

SN - 0006-2960

IS - 41

ER -