B American Society for Mass Spectrometry, 2017 J. Am. Soc. Mass Spectrom. (2017) 28:2658Y2664
The Effect of Salts in Promoting Specific
and Competitive Interactions between Zinc
Finger Proteins and Metals
Gongyu Li, Siming Yuan, Shihui Zheng, Yuting Chen, Zhen Zheng, Yangzhong Liu,
Department of Chemistry, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei,
Anhui 230026, People’sRepublicofChina
Abstract. Specific protein–metal interactions (PMIs) fulfill essential functions in cells
and organic bodies, and activation of these functions in vivo are mostly modulated by
the complex environmental factors, including pH value, small biomolecules, and
salts. Specifically, the role of salts in promoting specific PMIs and their competition
among various metals has remained untapped mainly due to the difficulty to distin-
guish nonspecific PMIs from specific PMIs by classic spectroscopic techniques.
Herein, we report Hofmeister salts differentially promote the specific PMIs by com-
bining nanoelectrospray ionization mass spectrometry and spectroscopic techniques
(fluorescence measurement and circular dichroism). Furthermore, to explore the
influence of salts in competitive binding between metalloproteins and various metals, we designed a series of
competitive experiments and applied to a well-defined model system, the competitive binding of zinc (II) and
arsenic (III) to holo-promyelocytic leukemia protein (PML). These experiments not only provided new insights at
the molecular scale as complementary to previous NMR and spectroscopic results, but also deduced the relative
binding ability between zinc finger proteins and metals at the molecular scale, which avoids the mass spectro-
metric titration-based determination of binding constants that is frequently affected and often degraded by
variable solution conditions including salt contents.
Keywords: Protein–metal interactions, Hofmeister salt, Zinc finger protein, Promyelocytic leukemia protein, Mass
Received: 13 May 2017/Revised: 1 August 2017/Accepted: 15 August 2017/Published Online: 8 September 2017
rotein–metal interactions (PMIs) have long been acknowl-
edged to be inextricably critical for many biological regu-
lations and disease developments [1–3]. For example, almost
half of all enzymes were found to be associated with at least
one particular metal to function properly . To understand
why each metal–protein partnership arose and how it is main-
tained has become increasingly important .
Hofmeister salts, including ammonium acetate (NH
have been increasingly investigated regarding the influence of
ions on the physical behavior of a wide variety of aqueous
processes, such as the Bsalting in^ and Bsalting out^ of proteins
. Actually, the stabilizing effect of Hofmeister salts for
multiprotein complex has been extensively investigated [5–
10]. However, the role of Hofmeister salts in promoting spe-
cific PMIs has not been systematically investigated so far,
although the solution conditions were reported with significant
influences on the PMIs .
Typical tools for PMI studies are spectroscopic measure-
ments, including fluorescence (FL), circular dichroism (CD)
[11, 12], and NMR [13–15] to reveal solution PMI structures.
Though great achievements have been made by these
pioneering techniques, it is still challenging to reveal specific
Gongyu Li and Siming Yuan contributed equally to this work.
Electronic supplementary material The online version of this article (https://
doi.org/10.1007/s13361-017-1789-6) contains supplementary material, which
is available to authorized users.
Correspondence to: Yangzhong Liu; e-mail: email@example.com, Guangming
Huang; e-mail: firstname.lastname@example.org