A proprietary shop is a "Tochtergesellschaft" = "Subsidiary" which only exists to provide a service or sell a product or service for the "Muttergesellschaft" = "parent company" in contrast to a subsidiary created to open up a new market or segment. Oil-multi owned petrol stations are examples of physical goods proprietary shops. Often we read about "Vertriebsgesellschaften" owned by the company which manufacturers the product sold by the "Vertriebsgeschellschaft".
The term "Proprietary shop" is almost never a compliment, in the old days, the subsidiaries mentioned above often did not have to worry about their own profitability because the parent company was just using them to "show the flag". This is still sometimes true of bank branches, Tschibo shops and petrol stations. The parent keeps one "shop" open in a town or village for appearances, whether it makes a profit or not.
In your case, X may want to make the custody unit (or the big bank, whichever is meant) more independent, faster, more flexible, quicker reacting and ultimately more profitable through the use of e-business and therefore less of a "proprietary shop" in the negative sense.
The following URLs show how the term is used but give no German translation:
"...Rowe thinks Puma's new Web-based service, and the company's years of experience, will keep it a step ahead of ... ... rival Starfish, part of Motorola (MOT) , Rowe is dismissive. He claims Starfish is limited mostly to supporting Motorola hardware, while Puma supports products from Nokia (NOK) , Ericsson, Motorola, NTT and Sprint. "We're the champion of the IT department and champion of the end-user, rather than a Motorola proprietary shop, which is what they are," he says."
The remaining area that this partnership does not address is the hybrid open-source nature of Sendmail and how that affects the product bundling with MessagingDirect, a proprietary shop. Sendmail has a hybrid model in that it supports open-source and publishes some of its source code, but, as in the case of the MessagingDirect partnership, also supports and sells proprietary code to which users don't have access.
Mr. Quinlan indicated that the Bureau wanted to state its overall IS strategy up front; they started a transformation in 1990 from an NCR proprietary shop by purchasing a Medicaid system from Consultec that runs on an IBM platform, and incorporating personal computers on local area networks into their offices.
I also have no German translation, maybe you or some other EN>GE translator can think of a term after reading the above. - HTH - Dan