Structural and functional characterizations of SsgB, a conserved activator of developmental cell division in morphologically complex actinomycetes.
SsgA-like proteins (SALPs) are a family of homologous cell division-related proteins that occur exclusively in morphologically complex actinomycetes. We show that SsgB, a subfamily of SALPs, is the archetypal SALP that is functionally conserved in all sporulating actinomycetes. Sporulation-specific cell division of Streptomyces coelicolor ssgB mutants is restored by introduction of distant ssgB orthologues from other actinomycetes. Interestingly, the number of septa (and spores) of the complemented null mutants is dictated by the specific ssgB orthologue that is expressed. The crystal structure of the SsgB from Thermobifida fusca was determined at 2.6 A resolution and represents the first structure for this family. The structure revealed similarities to a class of eukaryotic "whirly" single-stranded DNA/RNA-binding proteins. However, the electro-negative surface of the SALPs suggests that neither SsgB nor any of the other SALPs are likely to interact with nucleotide substrates. Instead, we show that a conserved hydrophobic surface is likely to be important for SALP function and suggest that proteins are the likely binding partners.
Xu
Qingping
Q
Joint Center for Structural Genomics, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
Traag
Bjørn A
BA
Willemse
Joost
J
McMullan
Daniel
D
Miller
Mitchell D
MD
Elsliger
Marc-André
MA
Abdubek
Polat
P
Astakhova
Tamara
T
Axelrod
Herbert L
HL
Bakolitsa
Constantina
C
Carlton
Dennis
D
Chen
Connie
C
Chiu
Hsiu-Ju
HJ
Chruszcz
Maksymilian
M
Clayton
Thomas
T
Das
Debanu
D
Deller
Marc C
MC
Duan
Lian
L
Ellrott
Kyle
K
Ernst
Dustin
D
Farr
Carol L
CL
Feuerhelm
Julie
J
Grant
Joanna C
JC
Grzechnik
Anna
A
Grzechnik
Slawomir K
SK
Han
Gye Won
GW
Jaroszewski
Lukasz
L
Jin
Kevin K
KK
Klock
Heath E
HE
Knuth
Mark W
MW
Kozbial
Piotr
P
Krishna
S Sri
SS
Kumar
Abhinav
A
Marciano
David
D
Minor
Wladek
W
Mommaas
A Mieke
AM
Morse
Andrew T
AT
Nigoghossian
Edward
E
Nopakun
Amanda
A
Okach
Linda
L
Oommachen
Silvya
S
Paulsen
Jessica
J
Puckett
Christina
C
Reyes
Ron
R
Rife
Christopher L
CL
Sefcovic
Natasha
N
Tien
Henry J
HJ
Trame
Christine B
CB
van den Bedem
Henry
H
Wang
Shuren
S
Weekes
Dana
D
Hodgson
Keith O
KO
Wooley
John
J
Deacon
Ashley M
AM
Godzik
Adam
A
Lesley
Scott A
SA
Wilson
Ian A
IA
van Wezel
Gilles P
GP
D039903:Actinobacteria / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology*; D001665:Binding Sites; D002455:Cell Division; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray / Q000379:methods; D004926:Escherichia coli / Q000378:metabolism; D005816:Genetic Complementation Test; D008856:Microscopy, Fluorescence / Q000379:methods; D008858:Microscopy, Phase-Contrast / Q000379:methods; D008969:Molecular Sequence Data; D009154:Mutation; D017386:Sequence Homology, Amino Acid; D013171:Spores, Bacterial
D001426:Bacterial Proteins; C462919:ssgB protein, Streptomyces coelicolor