Water stress proteins of Nostoc commune (Cyanobacteria) are secreted with UV-A/B-absorbing pigments and associate with 1,4-beta-D-xylanxylanohydrolase activity.
1994; Elsevier BV; Volume: 269; Issue: 10 Linguagem: Inglês
10.1016/s0021-9258(17)37347-7
ISSN1083-351X
AutoresDonna R. Hill, S.L. Hladun, Siegfried Scherer, Malcolm Potts,
Tópico(s)Aquatic Ecosystems and Phytoplankton Dynamics
ResumoAcidic water stress polypeptides (Wsp) with molecular masses of 33, 37 and 39 kDa are the most abundant soluble proteins in the cyanobacterium Nostoc commune.Wsp polypeptides and W-AB-absorbing pig- ments are secreted by cells, accumulate in the extracellular glycan sheath, and are released from desiccated colonies upon rehydration.No evidence was obtained for either glycosylation, phosphorylation, or acylation of Wsp polypeptides.NH2-terminal amino acid sequences of the 33-, 37-, and 39-kDa polypeptides were identical: Ala-Leu-5r-Gly-Tyr-Tr-ne-Gly-Glu-Gln-X-Ile-Gln-Asn-Pro-Ser-Asn-Pro-Ser-Asn-Gly-Lys-Gln.This consensus NH2-terminal sequence and an internal sequence (Glu-Ala-Arg-Val-Thr-Gly-Pro-Thr-Thr-Pro-Ile-Asp) showed homologies with the sequences of carbohydrate-modifying enzymes.Purified Wsp polypeptides associate with a 1,4-/3-~-xylanxylanohydrolase activity that was inhibited specifically by Wsp antiserum.In the absence of salt, Wsp polypeptides, and the water-soluble W-AB-absorbing pigments, form multimeric complexes through strong ionic interactions.A possible role is suggested for Wsp polypeptides in the synthesis andor modification of a xylose-containing W-"absorbing pigment.The removal of water from cells, the storage of cells in the air-dried state, and the rewetting of dried cells impose physiological constraints which relatively few organisms can tolerate.The molecular basis for desiccation tolerance remains poorly understood.Mechanisms which maintain the structural integrity of membranes appear to be of importance.Certain sugars, particularly trehalose, prevent damage from dehydration not only by inhibiting fusion between adjacent membrane vesicles during drying, but also by maintaining membrane lipids in a fluid phase in the absence of water (1, 2).The experimental evidence suggests that trehalose can stabilize cell membranes for short periods in air, but it cannot do so for extended periods.In the latter respect, other mechanisms must be important in the protection of cells from long term dehydration stress.The roles of water stress proteins remain cryptic.Of those organisms which express desiccation tolerance, certain cyanobacteria have a particularly marked capacity to do so.One form, Nostoc commune, has become a very useful model
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