The 20-kilodalton (kDa) human growth hormone (hGH) differs from the 22-kDa hGH in the complex formation with cell surface hGH receptor and hGH-binding protein circulating in human plasma.
In spite of recent advance in understanding of the stoichiometry of 22-kDa human GH (22K-hGH) with cell surface hGH receptor (hGHR) and hGH-binding protein (hGH-BP) circulating in human plasma, that of 20-kDa hGH (20K-hGH) is poorly understood. To clarify this, mouse pro-B Ba/F3 cells stably expressing the full-length hGHR (Ba/F3-hGHR) and both recombinant and native hGH-BP were used in this study. Cell proliferation assay revealed that the two hGH isoforms increased Ba/F3-hGHR cells to the same extent in a dose-dependent manner at 0.1 pM-10 nM. However, the self-inhibition observed in 20K-hGH at 5 microM was significantly less than that in 22K-hGH. Furthermore, addition of 1 and 10 nM recombinant hGH-BP caused a slight inhibition in 20K-hGH, but a drastic inhibition in 22K-hGH. Gel filtration chromatography of mixtures of 20K-hGH with recombinant hGH-BP clearly demonstrated that 20K-hGH formed a 1:2 (hGH:hGH-BP) complex efficiently but no detectable 1:1 complex in any conditions. Supporting data were also obtained with native hGH-BP. Computer-aided homology modeling of 20K-hGH has provided speculative data that the conformational change caused by deletion of 15 residues may occur only in the loop between helix 1 and helix 2, resulting in the reduction of its site 1 affinity. In conclusion, 20K-hGH possesses a unique property for forming a 1:2 complex to the same extent as 22K-hGH but has difficulty in forming a 1:1 complex, which might be attributed to the conformational change restricted to its site 1 region.
Wada
M
M
Life Science Laboratories, Mitsui Chemicals, Inc., Chiba, Japan.
Uchida
H
H
Ikeda
M
M
Tsunekawa
B
B
Naito
N
N
Banba
S
S
Tanaka
E
E
Hashimoto
Y
Y
Honjo
M
M
D000818:Animals; D002352:Carrier Proteins / Q000097:blood* / Q000502:physiology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002850:Chromatography, Gel; D004305:Dose-Response Relationship, Drug; D019382:Human Growth Hormone / Q000097:blood* / Q000502:physiology*; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D008958:Models, Molecular; D011986:Receptors, Somatotropin / Q000097:blood* / Q000502:physiology*; D017386:Sequence Homology, Amino Acid
D002352:Carrier Proteins; D046911:Macromolecular Substances; D011986:Receptors, Somatotropin; D019382:Human Growth Hormone; C051815:somatotropin-binding protein