The main advantage of Grid computing over other distributed computing paradigms is its capability to coordinate the access to data and resources in a virtual multi-institutional environment. To this end, the information system plays a decisive role in selecting the services that meet the applications' needs. This paper presents an information system for the Grid that provides transparent and scalable group communication services to standard Grid applications, with the objective of supporting dynamic collaborations that could help address problems that involve only some participants of a virtual organization. In particular, it enables more flexible delivery mechanisms, which allows applications to select the appropriate services before sending their data to the information system. This significantly enhances the protection of data from unauthorized access, and avoids the transmission of unnecessary messages over the network. The proposed information system is based on the use of XML technologies and replication. It introduces several new advanced features that are not currently supported as a whole by any Grid middleware, such as: several entry points to the information, persistent capabilities, support for advanced queries based on XQuery, and support for the industrial standard WS-Policy. The information system has been stress tested under realistic workloads in a Grid infrastructure with 50 sites. Scalability has been evaluated in up to 1000 messages that can be up to 10 KB in size each, updated with a frequency of 5 min.Initiative is a strong collaborative and cooperative link with the Portuguese National Grid Initiative through the IBERGRID agreement. This infrastructure is connected to the European Grid Infrastructure (EGI) [6]. The IBERGRID VO for Life Science applications (life.vo.ibergrid.eu) is an example of VO that has been created in the context of EGI to support the research activity in the life science community. This VO enables international collaboration in medical imaging, bioinformatics, and drug discovery.However, dynamic collaborations present a challenge to Grid information systems, because they do not provide a simple way to define special access rights agreed by part of the members of a VO. For example, in a system like VOMS [7], this problem occurs when two or more groups of the VO agree to collaborate on the achievement of a particular objective. Although this can be tackled through the use of thematic VO subgroups, this approach has the disadvantage of requiring the approval of an administrator of the VO (except for very few services such as file catalogues), and requires the reconfiguration of the infrastructure to support differentiation among groups. Moreover, any interaction with the membership to groups must be done through the VO admin role, but even so, the usage of groups to support temporal collaborations is a widely used feature (e.g., biomed VO, IBERGRID VOs) because users in the VO are normally authorized to access all the resources, regardless of the group that they belong to...