Hormonal Proteins and Peptides. Volume II

296 Pages·1973·15.048 MB·English

by  Li Choh-Hao

CONTMBUTORS
MiKLOS BODANSZKY
JOHANNES MEIENHOFER
J. RAMACHANDRAN
HORMONAL
PROTEINS AND
PEPTIDES
Edited by CHOH HAO LI
The Hormone Research Laboratory
University of California
San Francisco, California
VOLUME II
ACADEMIC PRESS New York and London 1973
A Subsidiary of Harcourt Brace Jovanovich, Publishers
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List of Contributors
Numbers in parentheses indicate the pages on which the authors' contributions begin.
MIKLOS BODANSZKY (29), Department of Chemistry, Case Western Re­
serve University, Cleveland, Ohio
JOHANNES MEIENHOFER (45), The Children's Cancer Research Founda­
tion, and Department of Biological Chemistry, Harvard Medical School,
Boston, Massachusetts
J. RAMACHANDRAN (1), The Hormone Research Laboratory, University
of California, San Francisco, California
Preface
As chemical compounds, mammalian hormones fall into three classes:
steroids, phenol derivatives, and proteins or polypeptides. Among these
hormonal compounds, protein and polypeptide hormones are most com­
plex and hence it is difficult to isolate them in pure form, to elucidate their
chemical structure, and to synthesize them in the laboratory. With the
remarkable development of various techniques for protein chemistry in the
last twenty years, our knowledge of the chemical natures of hormonal pro­
teins and peptides has increased enormously.
Since 1953, the structures of the following protein and peptide hor­
mones have been elucidated: oxytocin, vasopressin, gastrin, secretin,
glucagon, calcitonin, cholecystokinin-pancreozymin, insulin, parathormone,
proinsulin, human chorionic somatomammotropin, and human chorionic
gonadotropin. The ten adenohypophyseal hormones, namely, adrenocorti-
cotropin, α-melanotropin, /3-melanotropin, /3-lipotropin, γ-lipotropin,
growth hormone, prolactin, interstitial cell-stimulating hormone, follicle-
stimulating hormones, and thyrotropin, have been completely purified; the
amino acid sequences of nine of them, with the exception of follicle-stimu­
lating hormone, are known. In addition, two gjycoproteins possessing hor­
monal activities have been highly purified: thyroglobulin and pregnant
mare serum gonadotropin.
The purposes of this treatise are to review critically and extensively pres­
ent knowledge on the chemistry and biology of these hormones. Included
in each volume is one chapter on a general subject, which is considered to
be of special interest to investigators in the field.
Volume I is devoted chiefly to the chemistry of several hormonal gjyco-
proteins. Volume II includes one chapter on the solid-phase method of
peptide synthesis and two chapters on peptide hormones. It is hoped that
these and future volumes of this work will provide an important forum
between protein chemistry and experimental endocrinology.
CHOH HAO LI
ix
Contents of Volume I
1. The Chemistry of Glycoproteins
Richard /. Winzler
2. The Chemistry of Pituitary Thyrotropin
John G. Pierce, Ta-Hsiu Liao, and Robert B. Carlsen
3. The Chemistry of the Interstitial Cell-Stimulating Hormone of Ovine
Pituitary Origin
Harold Papkoff
4. The Biology of Pituitary Interstitial Cell-Stimulating Hormone
M. R. Sairam and Choh Hao Li
5. Chemistry of Human Chorionic Gonadotropin
Om P. Bahl
6. Chemistry and Biosynthesis of Thyroid Iodoproteins
G. Salvatore and H. Edelhoch
Author Index—Subject Index
XI
1
The Structure and Function
of Adrenocorticotropin
J. RAMACHANDRAN
I. Introduction 1
II. Structure of ACTH 2
III. Synthesis of ACTH and Related Peptides 4
IV. Biological Actions of ACTH 4
A. Actions on the Adrenal Cortex 4
B. Extra Adrenal Actions 5
C. Bioassays 6
V. Structure-Function Relationships 7
A. Adrenal-Stimulating Activity 7
B. Melanocyte Stimulating Activity 20
C. Lipolytic activity 21
VI. Conclusions 24
References 25
I. Introduction
Among the anterior pituitary hormones, adrenocorticotropin (ACTH)
has been investigated most extensively in terms of the relationship of the
structure of the hormone to the biological activities exhibited by the hor­
mone. Since the elucidation of the amino acid sequence of ACTH, several
reviews have appeared dealing with various aspects of the structure and
function of the hormone (Li, 1956, 1961, 1964; Hofmann, 1962; Hofmann
and Katsoyannis, 1963; Schwyzer, 1964; Dixon, 1964; Ramachandran and
Li, 1967). In recent years, significant progress has been achieved in eluci­
dating the biochemical mechanisms involved in the manifestation of the
physiological actions of ACTH (Grahame-Smith et al, 1967; Garren et al,
2 J. RAMACHANDRAN
1971 ). Attention is focused at the present time on the primary events in the
interaction of hormones with target cells with the aim of describing the
physicochemical mechanisms of hormone interaction with cellular receptors
which are viewed as complementary structures (Hechter and Halkerston,
1964). In this article, the structure-function relationships of ACTH will be
discussed with reference to the ability to stimulate the adrenal gland of the
rat, amphibian melanophores and adipose tissues of the rat and rabbit, em­
phasizing information gathered since the publication of the review by Rama-
chandran and Li (1967). The striking species specificity observed in the
responsiveness of rat and rabbit adipose tissues to ACTH and the
melanotropins is discussed in terms of the structural features of these hor­
mones. No attempt is made to list all the analogs of ACTH which have been
synthesized. In many instances, only a few chosen analogs are discussed
even though several others which have been prepared also prove the same
point.
The nomenclature employed in this article is that proposed by Li ( 1959).
The chain length of the peptides is indicated by a superscript and species
origin by a subscript. Thus ACTH isolated from sheep pituitaries is denoted
as «s1-39 ACTH. Since the first twenty-four residues are common to all
the known corticotropins, the species label is omitted in describing peptides
corresponding to segments in this portion of the molecule. Substitutions of
amino acid residues are indicated by a prefix containing the abbreviation for
the amino acid residue together with its position as a superscript. For in­
stance, replacement of histidine in position 6 by phenylalanine in the se­
quence of the nonadecapeptide corresponding to the first nineteen residues
of ACTH is denoted by Phe6 a1'19 ACTH. Multiple substitution such as
the replacement of serine in position 1 by D-serine and substitution of the
arginine residues in positions 17 and 18 by lysine in the tetracosapeptide
corresponding to the first twenty-four residues of ACTH is denoted by D-
Ser1, Lys 17»18 a124 ACTH.
II. Structure of ACTH
The isolation, purification, and elucidation of the amino acid sequences of
corticotropins from different species have been fully reviewed by Li
(1956). The structures of the ovine (I) (Li et al, 1955), porcine (III, IV)
(Howard et al, 1955), bovine (II) (Li et al, 1958), and human (V) (Lee
et al, 1961 ) hormones are shown in Fig. 1. All the hormones are composed
of thirty-nine amino acids with serine at the amino terminal and phenylalan­
ine at the carboxyl terminal. The structural differences between the hor­
mones are minor and are found in the portion of the polypeptide chain be­
tween the twenty-fourth and thirty-third amino acid residues. The structures
of porcine and human ACTH have been recently revised by Riniker et al
1. THE STRUCTURE AND FUNCTION OF ADRENOCORTICOTROPIN 3
(1972). The revisions are also indicated in Fig. 1. On the basis of the re­
vised structures the porcine and human hormones are seen to be very close­
ly related, the only structural difference between them being the replace­
ment of leucine in position 31 of the porcine hormone by serine in human
ACTH.
ACTH appears to exist as a highly flexible random coil in solution. A va­
riety of physicochemical measurements support this conclusion. The kinetics
of deuterium hydrogen exchange (Lindeström-Lang, quoted by Li, 1956;
Blout, quoted by Li, 1962), optical rotatory dispersion studies (Squire and
Bewley, 1965; Schwyzer and Sieber, 1966), circular dichroism, and fluores­
cence measurements (Edelhoch and Lippoldt, 1969) and fluorescence depo­
larization (Bernstein et al, 1969) of ACTH indicate that there are no rec­
ognizable intramolecular interactions in ACTH which stabilize structures
such as the a helix. Potentiometric titration of ACTH (Leonis and Li,
1959) as well as studies of the hydrodynamic properties (Squire and Li,
1961) indicated that the hormone may exist in a more compact conforma­
tion at slightly alkaline pH compared to acidic conditions. The only evi­
dence for some type of intramolecular interaction was presented by Eisinger
(1969) who found that the intramolecular distance between tyrosine in po­
sition 2 and the tryptophan residue in position 9, measured by the efficiency
Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-Gly-Lys-Lys-Arg-Arg-Pro
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Val-Lys-Val-Tyr-Pro Ala - Phe- Pro- Leu-Glu- Phe
20 21 22 23 24 34 35 36 37 38 39
Ovine (I) Ala- Gly - Glu- Asp- Asp- Glu- Ala- Ser- Gin Li, et al. (1955)
25 26 27 28 29 30 31 32 33
Bovine (II) Asp-Gly-Glu-Ala-Glu-Asp-Ser- Ala-Gin Li, etal. (1958)
Porcine (ΙΠ) Asp-Gly-Ala-Glu-Asp-Gin-Leu-Ala-Glu Howard, et al. (1955)
Porcine (IV) Asn - Gly - Ala- Glu- Asp- Glu- Leu - Ala- Glu Riniker, et al. (1972)
(revised)
Human (V) Asp-Ala-Gly-Glu-Asp-Gln-Ser-Ala-Glu Lee, et al. (1961)
Human (VI) Asn-Gly-Aia-Glu-Asp-Glu-Ser- Ala-Glu Riniker, et al. (1972)
(revised)
FIG. 1. Amino acid sequences of corticotropins of different species. The amino acid
sequences of the ovine and bovine hormones have also been revised recently (Li,
1972). The revised segments are:
Asp-Gly-Ala-Glu-Asp-Glu-Ser-Ala-Gln
25 26 27 28 29 30 31 31 32
in ovine ACTH and
Asn-Gly-Ala-Glu-Asp-Glu-Ser-Ala-Gln
25 26 27 28 29 30 31 32 33
in bovine ACTH.
4 J. RAMACHANDRAN
of energy transfer from tyrosine to tryptophan, was more consistent with
some form of loop or helical structure rather than a random coil between
residue 2 and 9. Synthetic peptides corresponding to segments of the first
twenty-four residues of ACTH were employed in these studies.
ΙΠ. Synthesis of ACTH and Related Peptides
Just as the determination of the amino acid sequence of ACTH in 1955
marked a major milestone in the study of polypeptide and protein structure,
the synthesis of a biologically active nonadecapeptide corresponding to the
first nineteen residues of ACTH by Li et al (1960) and the subsequent to­
tal synthesis of the porcine hormone (III) by Schwyzer and Sieber (1963),
constituted major advances in the field of polypeptide synthesis. The syn­
thesis of a peptide corresponding to the amino acid sequence of human
ACTH (V) was accomplished by Bajusz et al. (1967). A large number of
peptides corresponding to various segments of the polypeptide chain of
ACTH have diverse functions of this hormone with its structure. The syn­
thetic approach to the elucidation of the structure-function relationships of
ACTH and the melanotropins have been reviewed in detail (Ramachandran
and Li, 1967). All these peptides were synthesized by conventional methods
involving the careful isolation and purification of peptide intermediates. Re­
cently, the solid phase peptide synthesis introduced by Merrifield has been
utilized for the synthesis of peptides related to ACTH. Numerous synthetic
peptide analogs of ACTH have been prepared in the past 5 years. Several of
these analogs have been very useful in distinguishing those structural fea­
tures of the hormone essential for interaction with the target organ from the
features that contribute to the survival of the hormone in the biological envi­
ronment during transport. Some of the analogs have already been found
clinically useful. These aspects are discussed below.
IV. Biological Actions of ACTH
A. ACTIONS ON THE ADRENAL CORTEX
The major actions of ACTH on the adrenal cortex include hypertrophy
of the adrenals, repair of the histological changes produced in the adrenals
by hypophysectomy, depletion of adrenal ascorbic acid, and the stimulation
of corticosteroid synthesis. Since the report of Haynes and Berthet (1957)
implicating cyclic 3',5'-adenosine monophosphate (cyclic AMP) in adrenal
steroidogenesis, considerable evidence has been accumulated in support of
the thesis that all the actions of ACTH on the adrenal gland are mediated
by cyclic AMP. Thus, cyclic AMP was shown to induce steroidogenesis in